diff --git a/common/djangoapps/user_api/migrations/0002_auto__add_usercoursetags__add_unique_usercoursetags_user_course_id_key.py b/common/djangoapps/user_api/migrations/0002_auto__add_usercoursetags__add_unique_usercoursetags_user_course_id_key.py
new file mode 100644
index 0000000000..cc7e27cc4d
--- /dev/null
+++ b/common/djangoapps/user_api/migrations/0002_auto__add_usercoursetags__add_unique_usercoursetags_user_course_id_key.py
@@ -0,0 +1,87 @@
+# -*- coding: utf-8 -*-
+import datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+        # Adding model 'UserCourseTags'
+        db.create_table('user_api_usercoursetags', (
+            ('id', self.gf('django.db.models.fields.AutoField')(primary_key=True)),
+            ('user', self.gf('django.db.models.fields.related.ForeignKey')(related_name='+', to=orm['auth.User'])),
+            ('key', self.gf('django.db.models.fields.CharField')(max_length=255, db_index=True)),
+            ('course_id', self.gf('django.db.models.fields.CharField')(max_length=255, db_index=True)),
+            ('value', self.gf('django.db.models.fields.TextField')()),
+        ))
+        db.send_create_signal('user_api', ['UserCourseTags'])
+
+        # Adding unique constraint on 'UserCourseTags', fields ['user', 'course_id', 'key']
+        db.create_unique('user_api_usercoursetags', ['user_id', 'course_id', 'key'])
+
+
+    def backwards(self, orm):
+        # Removing unique constraint on 'UserCourseTags', fields ['user', 'course_id', 'key']
+        db.delete_unique('user_api_usercoursetags', ['user_id', 'course_id', 'key'])
+
+        # Deleting model 'UserCourseTags'
+        db.delete_table('user_api_usercoursetags')
+
+
+    models = {
+        'auth.group': {
+            'Meta': {'object_name': 'Group'},
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '80'}),
+            'permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'})
+        },
+        'auth.permission': {
+            'Meta': {'ordering': "('content_type__app_label', 'content_type__model', 'codename')", 'unique_together': "(('content_type', 'codename'),)", 'object_name': 'Permission'},
+            'codename': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['contenttypes.ContentType']"}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '50'})
+        },
+        'auth.user': {
+            'Meta': {'object_name': 'User'},
+            'date_joined': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'email': ('django.db.models.fields.EmailField', [], {'max_length': '75', 'blank': 'True'}),
+            'first_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'groups': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['auth.Group']", 'symmetrical': 'False', 'blank': 'True'}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_active': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_staff': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'is_superuser': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'last_login': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'last_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'password': ('django.db.models.fields.CharField', [], {'max_length': '128'}),
+            'user_permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '30'})
+        },
+        'contenttypes.contenttype': {
+            'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},
+            'app_label': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '100'})
+        },
+        'user_api.usercoursetags': {
+            'Meta': {'unique_together': "(('user', 'course_id', 'key'),)", 'object_name': 'UserCourseTags'},
+            'course_id': ('django.db.models.fields.CharField', [], {'max_length': '255', 'db_index': 'True'}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.CharField', [], {'max_length': '255', 'db_index': 'True'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "'+'", 'to': "orm['auth.User']"}),
+            'value': ('django.db.models.fields.TextField', [], {})
+        },
+        'user_api.userpreference': {
+            'Meta': {'unique_together': "(('user', 'key'),)", 'object_name': 'UserPreference'},
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.CharField', [], {'max_length': '255', 'db_index': 'True'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "'+'", 'to': "orm['auth.User']"}),
+            'value': ('django.db.models.fields.TextField', [], {})
+        }
+    }
+
+    complete_apps = ['user_api']
\ No newline at end of file
diff --git a/common/djangoapps/user_api/migrations/0003_rename_usercoursetags.py b/common/djangoapps/user_api/migrations/0003_rename_usercoursetags.py
new file mode 100644
index 0000000000..dc448817e3
--- /dev/null
+++ b/common/djangoapps/user_api/migrations/0003_rename_usercoursetags.py
@@ -0,0 +1,72 @@
+# -*- coding: utf-8 -*-
+import datetime
+from south.db import db
+from south.v2 import SchemaMigration
+from django.db import models
+
+
+class Migration(SchemaMigration):
+
+    def forwards(self, orm):
+        db.rename_table('user_api_usercoursetags', 'user_api_usercoursetag')
+
+
+    def backwards(self, orm):
+        db.rename_table('user_api_usercoursetag', 'user_api_usercoursetags')
+
+
+    models = {
+        'auth.group': {
+            'Meta': {'object_name': 'Group'},
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '80'}),
+            'permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'})
+        },
+        'auth.permission': {
+            'Meta': {'ordering': "('content_type__app_label', 'content_type__model', 'codename')", 'unique_together': "(('content_type', 'codename'),)", 'object_name': 'Permission'},
+            'codename': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'content_type': ('django.db.models.fields.related.ForeignKey', [], {'to': "orm['contenttypes.ContentType']"}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '50'})
+        },
+        'auth.user': {
+            'Meta': {'object_name': 'User'},
+            'date_joined': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'email': ('django.db.models.fields.EmailField', [], {'max_length': '75', 'blank': 'True'}),
+            'first_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'groups': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['auth.Group']", 'symmetrical': 'False', 'blank': 'True'}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'is_active': ('django.db.models.fields.BooleanField', [], {'default': 'True'}),
+            'is_staff': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'is_superuser': ('django.db.models.fields.BooleanField', [], {'default': 'False'}),
+            'last_login': ('django.db.models.fields.DateTimeField', [], {'default': 'datetime.datetime.now'}),
+            'last_name': ('django.db.models.fields.CharField', [], {'max_length': '30', 'blank': 'True'}),
+            'password': ('django.db.models.fields.CharField', [], {'max_length': '128'}),
+            'user_permissions': ('django.db.models.fields.related.ManyToManyField', [], {'to': "orm['auth.Permission']", 'symmetrical': 'False', 'blank': 'True'}),
+            'username': ('django.db.models.fields.CharField', [], {'unique': 'True', 'max_length': '30'})
+        },
+        'contenttypes.contenttype': {
+            'Meta': {'ordering': "('name',)", 'unique_together': "(('app_label', 'model'),)", 'object_name': 'ContentType', 'db_table': "'django_content_type'"},
+            'app_label': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'model': ('django.db.models.fields.CharField', [], {'max_length': '100'}),
+            'name': ('django.db.models.fields.CharField', [], {'max_length': '100'})
+        },
+        'user_api.usercoursetag': {
+            'Meta': {'unique_together': "(('user', 'course_id', 'key'),)", 'object_name': 'UserCourseTag'},
+            'course_id': ('django.db.models.fields.CharField', [], {'max_length': '255', 'db_index': 'True'}),
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.CharField', [], {'max_length': '255', 'db_index': 'True'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "'+'", 'to': "orm['auth.User']"}),
+            'value': ('django.db.models.fields.TextField', [], {})
+        },
+        'user_api.userpreference': {
+            'Meta': {'unique_together': "(('user', 'key'),)", 'object_name': 'UserPreference'},
+            'id': ('django.db.models.fields.AutoField', [], {'primary_key': 'True'}),
+            'key': ('django.db.models.fields.CharField', [], {'max_length': '255', 'db_index': 'True'}),
+            'user': ('django.db.models.fields.related.ForeignKey', [], {'related_name': "'+'", 'to': "orm['auth.User']"}),
+            'value': ('django.db.models.fields.TextField', [], {})
+        }
+    }
+
+    complete_apps = ['user_api']
\ No newline at end of file
diff --git a/common/djangoapps/user_api/models.py b/common/djangoapps/user_api/models.py
index 77ab4c6c95..48a85c2bc7 100644
--- a/common/djangoapps/user_api/models.py
+++ b/common/djangoapps/user_api/models.py
@@ -33,3 +33,17 @@ class UserPreference(models.Model):
             return user_pref.value
         except cls.DoesNotExist:
             return default
+
+
+class UserCourseTag(models.Model):
+    """
+    Per-course user tags, to be used by various things that want to store tags about
+    the user.  Added initially to store assignment to experimental groups.
+    """
+    user = models.ForeignKey(User, db_index=True, related_name="+")
+    key = models.CharField(max_length=255, db_index=True)
+    course_id = models.CharField(max_length=255, db_index=True)
+    value = models.TextField()
+
+    class Meta:
+        unique_together = ("user", "course_id", "key")
diff --git a/common/djangoapps/user_api/tests/test_user_service.py b/common/djangoapps/user_api/tests/test_user_service.py
new file mode 100644
index 0000000000..f63f702bcb
--- /dev/null
+++ b/common/djangoapps/user_api/tests/test_user_service.py
@@ -0,0 +1,34 @@
+"""
+Test the user service
+"""
+from django.test import TestCase
+
+from student.tests.factories import UserFactory
+from user_api import user_service
+
+
+class TestUserService(TestCase):
+    """
+    Test the user service
+    """
+    def setUp(self):
+        self.user = UserFactory.create()
+        self.course_id = 'test_org/test_course_number/test_run'
+        self.test_key = 'test_key'
+
+    def test_get_set_course_tag(self):
+        # get a tag that doesn't exist
+        tag = user_service.get_course_tag(self.user, self.course_id, self.test_key)
+        self.assertIsNone(tag)
+
+        # test setting a new key
+        test_value = 'value'
+        user_service.set_course_tag(self.user, self.course_id, self.test_key, test_value)
+        tag = user_service.get_course_tag(self.user, self.course_id, self.test_key)
+        self.assertEqual(tag, test_value)
+
+        #test overwriting an existing key
+        test_value = 'value2'
+        user_service.set_course_tag(self.user, self.course_id, self.test_key, test_value)
+        tag = user_service.get_course_tag(self.user, self.course_id, self.test_key)
+        self.assertEqual(tag, test_value)
diff --git a/common/djangoapps/user_api/user_service.py b/common/djangoapps/user_api/user_service.py
new file mode 100644
index 0000000000..a6355cd1ef
--- /dev/null
+++ b/common/djangoapps/user_api/user_service.py
@@ -0,0 +1,61 @@
+"""
+A service-like user_info interface.  Could be made into an http API later, but for now
+just in-process.  Exposes global and per-course key-value pairs for users.
+
+Implementation note:
+Stores global metadata using the UserPreference model, and per-course metadata using the
+UserCourseTag model.
+"""
+
+from user_api.models import UserCourseTag
+
+
+def get_course_tag(user, course_id, key):
+    """
+    Gets the value of the user's course tag for the specified key in the specified
+    course_id.
+
+    Args:
+        user: the User object for the course tag
+        course_id: course identifier (string)
+        key: arbitrary (<=255 char string)
+
+    Returns:
+        string value, or None if there is no value saved
+    """
+    try:
+        record = UserCourseTag.objects.get(
+            user=user,
+            course_id=course_id,
+            key=key)
+
+        return record.value
+    except UserCourseTag.DoesNotExist:
+        return None
+
+
+def set_course_tag(user, course_id, key, value):
+    """
+    Sets the value of the user's course tag for the specified key in the specified
+    course_id.  Overwrites any previous value.
+
+    The intention is that the values are fairly short, as they will be included in all
+    analytics events about this user.
+
+    Args:
+        user: the User object
+        course_id: course identifier (string)
+        key: arbitrary (<=255 char string)
+        value: arbitrary string
+    """
+
+    record, _ = UserCourseTag.objects.get_or_create(
+        user=user,
+        course_id=course_id,
+        key=key)
+
+    record.value = value
+    record.save()
+
+    # TODO: There is a risk of IntegrityErrors being thrown here given
+    # simultaneous calls from many processes.  Handle by retrying after a short delay?
diff --git a/common/lib/xmodule/setup.py b/common/lib/xmodule/setup.py
index f487081f8f..58d8170967 100644
--- a/common/lib/xmodule/setup.py
+++ b/common/lib/xmodule/setup.py
@@ -17,6 +17,7 @@ XMODULES = [
     "problem = xmodule.capa_module:CapaDescriptor",
     "problemset = xmodule.seq_module:SequenceDescriptor",
     "randomize = xmodule.randomize_module:RandomizeDescriptor",
+    "split_test = xmodule.split_test_module:SplitTestDescriptor",
     "section = xmodule.backcompat_module:SemanticSectionDescriptor",
     "sequential = xmodule.seq_module:SequenceDescriptor",
     "slides = xmodule.backcompat_module:TranslateCustomTagDescriptor",
diff --git a/common/lib/xmodule/xmodule/course_module.py b/common/lib/xmodule/xmodule/course_module.py
index c56569dd3a..c728da1cae 100644
--- a/common/lib/xmodule/xmodule/course_module.py
+++ b/common/lib/xmodule/xmodule/course_module.py
@@ -9,6 +9,7 @@ import dateutil.parser
 from lazy import lazy
 
 from xmodule.modulestore import Location
+from xmodule.partitions.partitions import UserPartition
 from xmodule.seq_module import SequenceDescriptor, SequenceModule
 from xmodule.graders import grader_from_conf
 import json
@@ -156,10 +157,27 @@ class TextbookList(List):
         return json_data
 
 
+class UserPartitionList(List):
+    def from_json(self, values):
+        return [UserPartition.from_json(v) for v in values]
+
+    def to_json(self, values):
+        return [user_partition.to_json()
+                for user_partition in values]
+
+
 class CourseFields(object):
     lti_passports = List(help="LTI tools passports as id:client_key:client_secret", scope=Scope.settings)
     textbooks = TextbookList(help="List of pairs of (title, url) for textbooks used in this course",
                              default=[], scope=Scope.content)
+
+    # This field is intended for Studio to update, not to be exposed directly via
+    # advanced_settings.
+    user_partitions = UserPartitionList(
+        help="List of user partitions of this course into groups, used e.g. for experiments",
+        default=[], scope=Scope.content)
+
+
     wiki_slug = String(help="Slug that points to the wiki for this course", scope=Scope.content)
     enrollment_start = Date(help="Date that enrollment for this class is opened", scope=Scope.settings)
     enrollment_end = Date(help="Date that enrollment for this class is closed", scope=Scope.settings)
@@ -354,7 +372,7 @@ class CourseFields(object):
         # Ensure that courses imported from XML keep their image
         default="images_course_image.jpg"
     )
-    
+
     ## Course level Certificate Name overrides.
     cert_name_short = String(
         help="Sitewide name of completion statements given to students (short).",
diff --git a/common/lib/xmodule/xmodule/modulestore/mongo/base.py b/common/lib/xmodule/xmodule/modulestore/mongo/base.py
index 6ee52a8b01..381292064f 100644
--- a/common/lib/xmodule/xmodule/modulestore/mongo/base.py
+++ b/common/lib/xmodule/xmodule/modulestore/mongo/base.py
@@ -321,13 +321,13 @@ class MongoModuleStore(ModuleStoreWriteBase):
         '''
         TODO (cdodge) This method can be deleted when the 'split module store' work has been completed
         '''
-
         # get all collections in the course, this query should not return any leaf nodes
         # note this is a bit ugly as when we add new categories of containers, we have to add it here
+
+        block_types_with_children = set(name for name, class_ in XBlock.load_classes() if getattr(class_, 'has_children', False))
         query = {'_id.org': location.org,
                  '_id.course': location.course,
-                 '_id.category': {'$in': ['course', 'chapter', 'sequential', 'vertical', 'videosequence',
-                                          'wrapper', 'problemset', 'conditional', 'randomize']}
+                 '_id.category': {'$in': list(block_types_with_children)}
                  }
         # we just want the Location, children, and inheritable metadata
         record_filter = {'_id': 1, 'definition.children': 1}
diff --git a/common/lib/xmodule/xmodule/partitions/__init__.py b/common/lib/xmodule/xmodule/partitions/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/common/lib/xmodule/xmodule/partitions/partitions.py b/common/lib/xmodule/xmodule/partitions/partitions.py
new file mode 100644
index 0000000000..e5d78b79e8
--- /dev/null
+++ b/common/lib/xmodule/xmodule/partitions/partitions.py
@@ -0,0 +1,116 @@
+"""Defines ``Group`` and ``UserPartition`` models for partitioning"""
+
+# We use ``id`` in this file as the IDs of our Groups and UserPartitions,
+# which Pylint disapproves of.
+# pylint: disable=invalid-name, redefined-builtin
+
+
+class Group(object):
+    """
+    An id and name for a group of students.  The id should be unique
+    within the UserPartition this group appears in.
+    """
+    # in case we want to add to this class, a version will be handy
+    # for deserializing old versions.  (This will be serialized in courses)
+    VERSION = 1
+
+    def __init__(self, id, name):
+        self.id = int(id)
+        self.name = name
+
+    def to_json(self):
+        """
+        'Serialize' to a json-serializable representation.
+
+        Returns:
+            a dictionary with keys for the properties of the group.
+        """
+        return {
+            "id": self.id,
+            "name": self.name,
+            "version": Group.VERSION
+        }
+
+    @staticmethod
+    def from_json(value):
+        """
+        Deserialize a Group from a json-like representation.
+
+        Args:
+            value: a dictionary with keys for the properties of the group.
+
+        Raises TypeError if the value doesn't have the right keys.
+        """
+        for key in ('id', 'name', 'version'):
+            if key not in value:
+                raise TypeError("Group dict {0} missing value key '{1}'".format(
+                    value, key))
+
+        if value["version"] != Group.VERSION:
+            raise TypeError("Group dict {0} has unexpected version".format(
+                value))
+
+        return Group(value["id"], value["name"])
+
+
+class UserPartition(object):
+    """
+    A named way to partition users into groups, primarily intended for running
+    experiments.  It is expected that each user will be in at most one group in a
+    partition.
+
+    A Partition has an id, name, description, and a list of groups.
+    The id is intended to be unique within the context where these are used. (e.g. for
+    partitions of users within a course, the ids should be unique per-course)
+    """
+    VERSION = 1
+
+    def __init__(self, id, name, description, groups):
+
+        self.id = int(id)
+        self.name = name
+        self.description = description
+        self.groups = groups
+
+    def to_json(self):
+        """
+        'Serialize' to a json-serializable representation.
+
+        Returns:
+            a dictionary with keys for the properties of the partition.
+        """
+        return {
+            "id": self.id,
+            "name": self.name,
+            "description": self.description,
+            "groups": [g.to_json() for g in self.groups],
+            "version": UserPartition.VERSION
+        }
+
+    @staticmethod
+    def from_json(value):
+        """
+        Deserialize a Group from a json-like representation.
+
+        Args:
+            value: a dictionary with keys for the properties of the group.
+
+        Raises TypeError if the value doesn't have the right keys.
+        """
+        for key in ('id', 'name', 'description', 'version', 'groups'):
+            if key not in value:
+                raise TypeError("UserPartition dict {0} missing value key '{1}'"
+                                .format(value, key))
+
+        if value["version"] != UserPartition.VERSION:
+            raise TypeError("UserPartition dict {0} has unexpected version"
+                            .format(value))
+
+        groups = [Group.from_json(g) for g in value["groups"]]
+
+        return UserPartition(
+            value["id"],
+            value["name"],
+            value["description"],
+            groups
+        )
diff --git a/common/lib/xmodule/xmodule/partitions/partitions_service.py b/common/lib/xmodule/xmodule/partitions/partitions_service.py
new file mode 100644
index 0000000000..3fb5f06e6c
--- /dev/null
+++ b/common/lib/xmodule/xmodule/partitions/partitions_service.py
@@ -0,0 +1,138 @@
+"""
+This is a service-like API that assigns tracks which groups users are in for various
+user partitions.  It uses the user_service key/value store provided by the LMS runtime to
+persist the assignments.
+"""
+import random
+from abc import ABCMeta, abstractproperty
+
+
+class PartitionService(object):
+    """
+    This is an XBlock service that assigns tracks which groups users are in for various
+    user partitions.  It uses the provided user_tags service object to
+    persist the assignments.
+    """
+    __metaclass__ = ABCMeta
+
+    @abstractproperty
+    def course_partitions(self):
+        """
+        Return the set of partitions assigned to self._course_id
+        """
+        raise NotImplementedError('Subclasses must implement course_partition')
+
+    def __init__(self, user_tags_service, course_id, track_function):
+        self.random = random.Random()
+        self._user_tags_service = user_tags_service
+        self._course_id = course_id
+        self._track_function = track_function
+
+    def get_user_group_for_partition(self, user_partition_id):
+        """
+        If the user is already assigned to a group in user_partition_id, return the
+        group_id.
+
+        If not, assign them to one of the groups, persist that decision, and
+        return the group_id.
+
+        If the group they are assigned to doesn't exist anymore, re-assign to one of
+        the existing groups and return its id.
+
+        Args:
+            user_partition_id -- an id of a partition that's hopefully in the
+                runtime.user_partitions list.
+
+        Returns:
+            The id of one of the groups in the specified user_partition_id (as a string).
+
+        Raises:
+            ValueError if the user_partition_id isn't found.
+        """
+        user_partition = self._get_user_partition(user_partition_id)
+        if user_partition is None:
+            raise ValueError(
+                "Configuration problem!  No user_partition with id {0} "
+                "in course {1}".format(user_partition_id, self._course_id)
+            )
+
+        group_id = self._get_group(user_partition)
+
+        return group_id
+
+    def _get_user_partition(self, user_partition_id):
+        """
+        Look for a user partition with a matching id in
+        in the course's partitions.
+
+        Returns:
+            A UserPartition, or None if not found.
+        """
+        for partition in self.course_partitions:
+            if partition.id == user_partition_id:
+                return partition
+
+        return None
+
+    def _key_for_partition(self, user_partition):
+        """
+        Returns the key to use to look up and save the user's group for a particular
+        condition.  Always use this function rather than constructing the key directly.
+        """
+        return 'xblock.partition_service.partition_{0}'.format(user_partition.id)
+
+    def _get_group(self, user_partition):
+        """
+        Return the group of the current user in user_partition.  If they don't already have
+        one assigned, pick one and save it.  Uses the runtime's user_service service to look up
+        and persist the info.
+        """
+        key = self._key_for_partition(user_partition)
+        scope = self._user_tags_service.COURSE
+
+        group_id = self._user_tags_service.get_tag(scope, key)
+        if group_id is not None:
+            group_id = int(group_id)
+
+        partition_group_ids = [group.id for group in user_partition.groups]
+
+        # If a valid group id has been saved already, return it
+        if group_id is not None and group_id in partition_group_ids:
+            return group_id
+
+        # TODO: what's the atomicity of the get above and the save here?  If it's not in a
+        # single transaction, we could get a situation where the user sees one state in one
+        # thread, but then that decision gets overwritten--low probability, but still bad.
+
+        # (If it is truly atomic, we should be fine--if one process is in the
+        # process of finding no group and making one, the other should block till it
+        # appears.  HOWEVER, if we allow reads by the second one while the first
+        # process runs the transaction, we have a problem again: could read empty,
+        # have the first transaction finish, and pick a different group in a
+        # different process.)
+
+        # If a group id hasn't yet been saved, or the saved group id is invalid,
+        # we need to pick one, save it, then return it
+
+        # TODO: had a discussion in arch council about making randomization more
+        # deterministic (e.g. some hash).  Could do that, but need to be careful not
+        # to introduce correlation between users or bias in generation.
+
+        # See note above for explanation of local_random()
+        group = self.random.choice(user_partition.groups)
+        self._user_tags_service.set_tag(scope, key, group.id)
+
+        # emit event for analytics
+        # FYI - context is always user ID that is logged in, NOT the user id that is
+        # being operated on. If instructor can move user explicitly, then we should
+        # put in event_info the user id that is being operated on.
+        event_info = {
+            'group_id': group.id,
+            'group_name': group.name,
+            'partition_id': user_partition.id,
+            'partition_name': user_partition.name
+        }
+        # TODO: Use the XBlock publish api instead
+        self._track_function('edx.split_test.assigned_user_to_partition', event_info)
+
+        return group.id
diff --git a/common/lib/xmodule/xmodule/partitions/test_partitions.py b/common/lib/xmodule/xmodule/partitions/test_partitions.py
new file mode 100644
index 0000000000..d468af307b
--- /dev/null
+++ b/common/lib/xmodule/xmodule/partitions/test_partitions.py
@@ -0,0 +1,155 @@
+"""
+Test the partitions and partitions service
+
+"""
+
+from unittest import TestCase
+from mock import Mock, MagicMock
+
+from xmodule.partitions.partitions import Group, UserPartition
+from xmodule.partitions.partitions_service import PartitionService
+
+
+class TestGroup(TestCase):
+    """Test constructing groups"""
+    def test_construct(self):
+        test_id = 10
+        name = "Grendel"
+        group = Group(test_id, name)
+        self.assertEqual(group.id, test_id)
+        self.assertEqual(group.name, name)
+
+    def test_string_id(self):
+        test_id = "10"
+        name = "Grendel"
+        group = Group(test_id, name)
+        self.assertEqual(group.id, 10)
+
+    def test_to_json(self):
+        test_id = 10
+        name = "Grendel"
+        group = Group(test_id, name)
+        jsonified = group.to_json()
+        act_jsonified = {
+            "id": test_id,
+            "name": name,
+            "version": group.VERSION
+        }
+        self.assertEqual(jsonified, act_jsonified)
+
+    def test_from_json(self):
+        test_id = 5
+        name = "Grendel"
+        jsonified = {
+            "id": test_id,
+            "name": name,
+            "version": Group.VERSION
+        }
+        group = Group.from_json(jsonified)
+        self.assertEqual(group.id, test_id)
+        self.assertEqual(group.name, name)
+
+
+class StaticPartitionService(PartitionService):
+    """
+    Mock PartitionService for testing.
+    """
+    def __init__(self, partitions, **kwargs):
+        super(StaticPartitionService, self).__init__(**kwargs)
+        self._partitions = partitions
+
+    @property
+    def course_partitions(self):
+        return self._partitions
+
+
+class TestPartitionsService(TestCase):
+    """
+    Test getting a user's group out of a partition
+
+    """
+
+    def setUp(self):
+        groups = [Group(0, 'Group 1'), Group(1, 'Group 2')]
+        self.partition_id = 0
+
+        # construct the user_service
+        self.user_tags = dict()
+        self.user_tags_service = MagicMock()
+
+        def mock_set_tag(_scope, key, value):
+            """Sets the value of ``key`` to ``value``"""
+            self.user_tags[key] = value
+
+        def mock_get_tag(_scope, key):
+            """Gets the value of ``key``"""
+            if key in self.user_tags:
+                return self.user_tags[key]
+            return None
+
+        self.user_tags_service.set_tag = mock_set_tag
+        self.user_tags_service.get_tag = mock_get_tag
+
+        user_partition = UserPartition(self.partition_id, 'Test Partition', 'for testing purposes', groups)
+        self.partitions_service = StaticPartitionService(
+            [user_partition],
+            user_tags_service=self.user_tags_service,
+            course_id=Mock(),
+            track_function=Mock()
+        )
+
+    def test_get_user_group_for_partition(self):
+        # get a group assigned to the user
+        group1 = self.partitions_service.get_user_group_for_partition(self.partition_id)
+
+        # make sure we get the same group back out if we try a second time
+        group2 = self.partitions_service.get_user_group_for_partition(self.partition_id)
+
+        self.assertEqual(group1, group2)
+
+        # test that we error if given an invalid partition id
+        with self.assertRaises(ValueError):
+            self.partitions_service.get_user_group_for_partition(3)
+
+    def test_user_in_deleted_group(self):
+        # get a group assigned to the user - should be group 0 or 1
+        old_group = self.partitions_service.get_user_group_for_partition(self.partition_id)
+        self.assertIn(old_group, [0, 1])
+
+        # Change the group definitions! No more group 0 or 1
+        groups = [Group(3, 'Group 3'), Group(4, 'Group 4')]
+        user_partition = UserPartition(self.partition_id, 'Test Partition', 'for testing purposes', groups)
+        self.partitions_service = StaticPartitionService(
+            [user_partition],
+            user_tags_service=self.user_tags_service,
+            course_id=Mock(),
+            track_function=Mock()
+        )
+
+        # Now, get a new group using the same call - should be 3 or 4
+        new_group = self.partitions_service.get_user_group_for_partition(self.partition_id)
+        self.assertIn(new_group, [3, 4])
+
+        # We should get the same group over multiple calls
+        new_group_2 = self.partitions_service.get_user_group_for_partition(self.partition_id)
+        self.assertEqual(new_group, new_group_2)
+
+    def test_change_group_name(self):
+        # Changing the name of the group shouldn't affect anything
+        # get a group assigned to the user - should be group 0 or 1
+        old_group = self.partitions_service.get_user_group_for_partition(self.partition_id)
+        self.assertIn(old_group, [0, 1])
+
+        # Change the group names
+        groups = [Group(0, 'Group 0'), Group(1, 'Group 1')]
+        user_partition = UserPartition(self.partition_id, 'Test Partition', 'for testing purposes', groups)
+        self.partitions_service = StaticPartitionService(
+            [user_partition],
+            user_tags_service=self.user_tags_service,
+            course_id=Mock(),
+            track_function=Mock()
+        )
+
+        # Now, get a new group using the same call
+        new_group = self.partitions_service.get_user_group_for_partition(self.partition_id)
+        self.assertEqual(old_group, new_group)
diff --git a/common/lib/xmodule/xmodule/public/js/split_test_staff.js b/common/lib/xmodule/xmodule/public/js/split_test_staff.js
new file mode 100644
index 0000000000..8dd68bced6
--- /dev/null
+++ b/common/lib/xmodule/xmodule/public/js/split_test_staff.js
@@ -0,0 +1,43 @@
+
+/**
+ * Creates a new selector for managing toggling which child to show
+ * @constructor
+ */
+
+function ABTestSelector(elem) {
+    me = this;
+    me.elem = $(elem);
+
+    select_child = function(group_id) {
+        // iterate over all the children and hide all the ones that haven't been selected
+        // and show the one that was selected
+        me.elem.find('.split-test-child').each(function() {
+            // force this id to remain a string, even if it looks like something else
+            child_group_id = $(this).data('group-id').toString();
+            if(child_group_id === group_id) {
+                $(this).show();
+            }
+            else {
+                $(this).hide();
+            }
+
+        });
+    }
+
+    // hide all the children
+    me.elem.find('.split-test-child').hide();
+
+    select = me.elem.find('.split-test-select');
+    cur_group_id = select.val();
+    select_child(cur_group_id);
+
+    // bind the change event to the dropdown
+    select.change(function() {
+        group_id = $(this).val()
+        select_child(group_id);
+    });
+
+}
+
+
+
diff --git a/common/lib/xmodule/xmodule/split_test_module.py b/common/lib/xmodule/xmodule/split_test_module.py
new file mode 100644
index 0000000000..45440a9edf
--- /dev/null
+++ b/common/lib/xmodule/xmodule/split_test_module.py
@@ -0,0 +1,185 @@
+"""
+Module for running content split tests
+"""
+
+import logging
+
+from xmodule.progress import Progress
+from xmodule.seq_module import SequenceDescriptor
+from xmodule.x_module import XModule, module_attr
+
+from lxml import etree
+
+from xblock.core import XBlock
+from xblock.fields import Scope, Integer, Dict
+from xblock.fragment import Fragment
+
+log = logging.getLogger('edx.' + __name__)
+
+
+class SplitTestFields(object):
+    user_partition_id = Integer(help="Which user partition is used for this test",
+                                scope=Scope.content)
+
+    # group_id is an int
+    # child is a serialized UsageId (aka Location).  This child
+    # location needs to actually match one of the children of this
+    # Block.  (expected invariant that we'll need to test, and handle
+    # authoring tools that mess this up)
+
+    # TODO: is there a way to add some validation around this, to
+    # be run on course load or in studio or ....
+
+    group_id_to_child = Dict(help="Which child module students in a particular "
+                             "group_id should see",
+                             scope=Scope.content)
+
+
+@XBlock.needs('user_tags')
+@XBlock.needs('partitions')
+class SplitTestModule(SplitTestFields, XModule):
+    """
+    Show the user the appropriate child.  Uses the ExperimentState
+    API to figure out which child to show.
+
+    Course staff still get put in an experimental condition, but have the option
+    to see the other conditions.  The only thing that counts toward their
+    grade/progress is the condition they are actually in.
+
+    Technical notes:
+      - There is more dark magic in this code than I'd like.  The whole varying-children +
+        grading interaction is a tangle between super and subclasses of descriptors and
+        modules.
+"""
+    def __init__(self, *args, **kwargs):
+
+        super(SplitTestModule, self).__init__(*args, **kwargs)
+
+        self.child_descriptor = self.get_child_descriptors()[0]
+        if self.child_descriptor is not None:
+            self.child = self.system.get_module(self.child_descriptor)
+        else:
+            self.child = None
+
+    def get_child_descriptor_by_location(self, location):
+        """
+        Look through the children and look for one with the given location.
+        Returns the descriptor.
+        If none match, return None
+        """
+        # NOTE: calling self.get_children() creates a circular reference--
+        # it calls get_child_descriptors() internally, but that doesn't work until
+        # we've picked a choice.  Use self.descriptor.get_children() instead.
+
+        for child in self.descriptor.get_children():
+            if child.location.url() == location:
+                return child
+
+        return None
+
+    def get_child_descriptors(self):
+        """
+        For grading--return just the chosen child.
+        """
+        group_id = self.runtime.service(self, 'partitions').get_user_group_for_partition(self.user_partition_id)
+
+        # group_id_to_child comes from json, so it has to have string keys
+        str_group_id = str(group_id)
+        if str_group_id in self.group_id_to_child:
+            child_location = self.group_id_to_child[str_group_id]
+            child_descriptor = self.get_child_descriptor_by_location(child_location)
+        else:
+            # Oops.  Config error.
+            log.debug("configuration error in split test module: invalid group_id %r (not one of %r).  Showing error", str_group_id, self.group_id_to_child.keys())
+
+        if child_descriptor is None:
+            # Peak confusion is great.  Now that we set child_descriptor,
+            # get_children() should return a list with one element--the
+            # xmodule for the child
+            log.debug("configuration error in split test module: no such child")
+            return []
+
+        return [child_descriptor]
+
+    def _staff_view(self, context):
+        """
+        Render the staff view for a split test module.
+        """
+        fragment = Fragment()
+        contents = []
+
+        for group_id in self.group_id_to_child:
+            child_location = self.group_id_to_child[group_id]
+            child_descriptor = self.get_child_descriptor_by_location(child_location)
+            child = self.system.get_module(child_descriptor)
+            rendered_child = child.render('student_view', context)
+            fragment.add_frag_resources(rendered_child)
+
+            contents.append({
+                'group_id': group_id,
+                'id': child.id,
+                'content': rendered_child.content
+            })
+
+        # Use the new template
+        fragment.add_content(self.system.render_template('split_test_staff_view.html', {
+            'items': contents,
+        }))
+        frag_js = """
+            $(document).ready(function() {{
+                ABTestSelector($('.split-test-view'));
+            }});
+        """
+        fragment.add_javascript(frag_js)
+        fragment.add_javascript_url(self.runtime.local_resource_url(self, 'public/js/split_test_staff.js'))
+        return fragment
+
+    def student_view(self, context):
+        """
+        Render the contents of the chosen condition for students, and all the
+        conditions for staff.
+        """
+        if self.child is None:
+            # raise error instead?  In fact, could complain on descriptor load...
+            return Fragment(content=u"<div>Nothing here.  Move along.</div>")
+
+        if self.system.user_is_staff:
+            return self._staff_view(context)
+        else:
+            return self.child.render('student_view', context)
+
+    def get_icon_class(self):
+        return self.child.get_icon_class() if self.child else 'other'
+
+    def get_progress(self):
+        children = self.get_children()
+        progresses = [child.get_progress() for child in children]
+        progress = reduce(Progress.add_counts, progresses, None)
+        return progress
+
+
+@XBlock.needs('user_tags')
+@XBlock.needs('partitions')
+class SplitTestDescriptor(SplitTestFields, SequenceDescriptor):
+    # the editing interface can be the same as for sequences -- just a container
+    module_class = SplitTestModule
+
+    filename_extension = "xml"
+
+    child_descriptor = module_attr('child_descriptor')
+
+    def definition_to_xml(self, resource_fs):
+
+        xml_object = etree.Element('split_test')
+        # TODO: also save the experiment id and the condition map
+        for child in self.get_children():
+            xml_object.append(
+                etree.fromstring(child.export_to_xml(resource_fs)))
+        return xml_object
+
+    def has_dynamic_children(self):
+        """
+        Grading needs to know that only one of the children is actually "real".  This
+        makes it use module.get_child_descriptors().
+        """
+        return True
diff --git a/common/lib/xmodule/xmodule/tests/test_split_module.py b/common/lib/xmodule/xmodule/tests/test_split_module.py
new file mode 100644
index 0000000000..de82427042
--- /dev/null
+++ b/common/lib/xmodule/xmodule/tests/test_split_module.py
@@ -0,0 +1,74 @@
+"""
+Tests for the Split Testing Module
+"""
+import ddt
+from mock import Mock
+
+from xmodule.tests.xml import factories as xml
+from xmodule.tests.xml import XModuleXmlImportTest
+from xmodule.tests import get_test_system
+from xmodule.partitions.partitions import Group, UserPartition
+from xmodule.partitions.partitions_service import PartitionService
+from xmodule.partitions.test_partitions import StaticPartitionService
+
+
+
+class SplitTestModuleFactory(xml.XmlImportFactory):
+    """
+    Factory for generating SplitTestModules for testing purposes
+    """
+    tag = 'split_test'
+
+
+@ddt.ddt
+class SplitTestModuleTest(XModuleXmlImportTest):
+    """
+    Test the split test module
+    """
+
+    def setUp(self):
+        self.course_id = 'test_org/test_course_number/test_run'
+        # construct module
+        course = xml.CourseFactory.build()
+        sequence = xml.SequenceFactory.build(parent=course)
+        split_test = SplitTestModuleFactory(
+            parent=sequence,
+            attribs={
+                'user_partition_id': '0',
+                'group_id_to_child': '{"0": "i4x://edX/xml_test_course/html/split_test_cond0", "1": "i4x://edX/xml_test_course/html/split_test_cond1"}'
+            }
+        )
+        xml.HtmlFactory(parent=split_test, url_name='split_test_cond0')
+        xml.HtmlFactory(parent=split_test, url_name='split_test_cond1')
+
+        self.course = self.process_xml(course)
+        course_seq = self.course.get_children()[0]
+        self.module_system = get_test_system()
+
+        self.tags_service = Mock(name='user_tags')
+        self.module_system._services['user_tags'] = self.tags_service
+
+        self.partitions_service = StaticPartitionService(
+            [
+                UserPartition(0, 'first_partition', 'First Partition', [Group("0", 'alpha'), Group("1", 'beta')]),
+                UserPartition(1, 'second_partition', 'Second Partition', [Group("0", 'abel'), Group("1", 'baker'), Group("2", 'charlie')])
+            ],
+            user_tags_service=self.tags_service,
+            course_id=self.course.id,
+            track_function=Mock(name='track_function'),
+        )
+        self.module_system._services['partitions'] = self.partitions_service
+
+
+        self.split_test_descriptor = course_seq.get_children()[0]
+        self.split_test_descriptor.bind_for_student(
+            self.module_system,
+            self.split_test_descriptor._field_data
+        )
+
+    @ddt.data(('0', 'split_test_cond0'), ('1', 'split_test_cond1'))
+    @ddt.unpack
+    def test_child(self, user_tag, child_url_name):
+        self.tags_service.get_tag.return_value = user_tag
+
+        self.assertEquals(self.split_test_descriptor.child_descriptor.url_name, child_url_name)
diff --git a/common/lib/xmodule/xmodule/tests/xml/factories.py b/common/lib/xmodule/xmodule/tests/xml/factories.py
index a66fdba2e1..ec8020b44e 100644
--- a/common/lib/xmodule/xmodule/tests/xml/factories.py
+++ b/common/lib/xmodule/xmodule/tests/xml/factories.py
@@ -72,6 +72,7 @@ class XmlImportFactory(Factory):
     url_name = Sequence(str)
     attribs = {}
     policy = {}
+    inline_xml = True
     tag = 'unknown'
 
     @classmethod
@@ -95,10 +96,26 @@ class XmlImportFactory(Factory):
         kwargs['xml_node'].text = kwargs.pop('text', None)
 
         kwargs['xml_node'].attrib.update(kwargs.pop('attribs', {}))
+
+        # Make sure that the xml_module doesn't try and open a file to find the contents
+        # of this node.
+        inline_xml = kwargs.pop('inline_xml')
+
+        if inline_xml:
+            kwargs['xml_node'].set('not_a_pointer', 'true')
+
         for key in kwargs.keys():
             if key not in XML_IMPORT_ARGS:
                 kwargs['xml_node'].set(key, kwargs.pop(key))
 
+        if not inline_xml:
+            kwargs['xml_node'].write(
+                kwargs['filesystem'].open(
+                    '{}/{}.xml'.format(kwargs['tag'], kwargs['url_name'])
+                ),
+                encoding='utf-8'
+            )
+
         return kwargs
 
     @lazy_attribute
@@ -134,3 +151,8 @@ class ProblemFactory(XmlImportFactory):
     """Factory for <problem> nodes"""
     tag = 'problem'
     text = '<h1>Empty Problem!</h1>'
+
+
+class HtmlFactory(XmlImportFactory):
+    """Factory for <problem> nodes"""
+    tag = 'html'
diff --git a/docs/developers/source/experiments.rst b/docs/developers/source/experiments.rst
new file mode 100644
index 0000000000..8ac2caefe9
--- /dev/null
+++ b/docs/developers/source/experiments.rst
@@ -0,0 +1,76 @@
+*******************************************
+Content experiments
+*******************************************
+
+This is a brief overview of the support for content experiments in the platform.
+
+For now, there is only one type of experiment: content split testing.  This lets course authors define an experiment with several *experimental conditions*, add xblocks that reference that experiment in various places in the course, and specify what content students in each experimental condition should see.  The LMS provides a way to randomly assign students to experimental conditions for each experiment, so that they see the right content at runtime.
+
+Experimental conditions are essentially just a set of groups to partition users into.  This may be useful to other non-experiment uses, so the implementation is done via a generic UserPartition interface.  Copying the doc string, a UserPartition is:
+
+    A named way to partition users into groups, primarily intended for running
+    experiments.  It is expected that each user will be in at most one group in a
+    partition.
+
+    A Partition has an id, name, description, and a list of groups.
+    The id is intended to be unique within the context where these are used. (e.g. for
+    partitions of users within a course, the ids should be unique per-course)
+
+There is an XModule helper library ``partitions_service`` that helps manage user partitions from XBlocks (at the moment just from the split_test module).  It provides an interface to store and retrieve the groups a user is in for particular partitions.  
+
+User assignments to particular groups within a partition must be persisted.  This is done via a User Info service provided by the XBlock runtime, which exposes a generic user tagging interface, allowing storing key-value pairs for the user scoped to a particular course.
+
+UserPartitions are configured at the course level (makes sense in Studio, for author context, and there's no XBlock scope to store per-course configuration state), and currently exposed via the LMS XBlock runtime as ``runtime.user_partitions``.
+
+More details on the components below.
+
+
+User metadata service
+---------------------
+
+Goals: provide a standard way to store information about users, to be used e.g. by XBlocks, and make that information easily accessible when looking at analytics.
+
+When the course context is added to the analytics events, it should add the user's course-specific tags as well.
+When the users global context is added to analytics events, it should add the user's global tags.
+
+We have a ``user_api`` app, which has REST interface to "User Preferences" for global preferences, and now a ``user_service.py`` interface that exposes per-course tags, with string keys (<=255 chars) and arbitrary string values. The intention is that the values are fairly short, as they will be included in all analytics events about this user.
+
+The XBlock runtime includes a ``UserServiceInterface`` mixin that provides access to this interface, automatically filling in the current user and course context.  This means that with the current design, an XBlock can't access tags for other users or from other courses.
+
+To avoid name collisions in the keys, we rely on convention. e.g. the XBlock partition service uses ``'xblock.partition_service.partition_{0}'.format(user_partition.id)``.
+
+
+
+Where the code is:
+----------------
+
+
+common:
+
+- partitions library--defines UserPartitions, provides partitions_service API.
+- split_test_module -- a block that has one child per experimental condition (could be a vertical or other container with more blocks inside), and config specifying which child corresponds to which condition.
+- course_module -- a course has a list of UserPartitions, each of which specifies the set of groups to divide users into.
+
+LMS:
+
+- runtime--LmsUserPartitions, UserServiceMixin mixins.  Provides a way for the partition_service to get the list of UserPartitions defined in a course, and get/set per-user tags within a course scope.
+- user_api app -- provides persistence for the user tags.
+
+Things to watch out for (some not implemented yet):
+-------------------------------------------
+
+- grade export needs to be smarter, because different students can see different graded things
+- grading needs to only grade the children that a particular student sees (so if there are problems in both conditions in a split_test, any student would see only one set)
+- ui -- icons in sequences need to be passed through
+   - tooltips need to be passed through
+- author changes post-release: conditions can be added or deleted after an experiment is live.  This is usually a bad idea, but can be useful, so it's allowed.  Need to handle all the cases.
+- analytics logging needs to log all the user tags (if we really think it's a good idea).  We'll probably want to cache the tags in memory for the duration of the request, being careful that they may change as the request is processed.
+- need to add a "hiding" interface to XBlocks that verticals, sequentials, and courses understand, to hide children that set it.  Then give the split test module a way to say that particular condition should be empty and hidden, and pass that up.
+- staff view should show all the conditions, clearly marked
+ 
+Things to test:
+  - randomization
+  - persistence
+  - correlation between test that use the same groups
+  - non-correlation between tests that use different groups
+
diff --git a/docs/en_us/developers/source/index.rst b/docs/en_us/developers/source/index.rst
index cdd069ed19..bdda890114 100644
--- a/docs/en_us/developers/source/index.rst
+++ b/docs/en_us/developers/source/index.rst
@@ -24,6 +24,7 @@ APIs
 
     djangoapps.rst
     common-lib.rst
+    experiments.rst
 
 Internationalization
 ---------------------
diff --git a/lms/lib/xblock/runtime.py b/lms/lib/xblock/runtime.py
index c905e098d4..9c1692123c 100644
--- a/lms/lib/xblock/runtime.py
+++ b/lms/lib/xblock/runtime.py
@@ -6,7 +6,10 @@ import re
 
 from django.core.urlresolvers import reverse
 
+from user_api import user_service
+from xmodule.modulestore.django import modulestore
 from xmodule.x_module import ModuleSystem
+from xmodule.partitions.partitions_service import PartitionService
 
 
 def _quote_slashes(match):
@@ -109,8 +112,77 @@ class LmsHandlerUrls(object):
         })
 
 
+class LmsPartitionService(PartitionService):
+    """
+    Another runtime mixin that provides access to the student partitions defined on the
+    course.
+
+    (If and when XBlock directly provides access from one block (e.g. a split_test_module)
+    to another (e.g. a course_module), this won't be neccessary, but for now it seems like
+    the least messy way to hook things through)
+
+    """
+    @property
+    def course_partitions(self):
+        course = modulestore().get_course(self._course_id)
+        return course.user_partitions
+
+
+class UserTagsService(object):
+    """
+    A runtime class that provides an interface to the user service.  It handles filling in
+    the current course id and current user.
+    """
+    # Scopes
+    # (currently only allows per-course tags.  Can be expanded to support
+    # global tags (e.g. using the existing UserPreferences table))
+    COURSE = 'course'
+
+    def __init__(self, runtime):
+        self.runtime = runtime
+
+    def _get_current_user(self):
+        real_user = self.runtime.get_real_user(self.runtime.anonymous_student_id)
+        return real_user
+
+    def get_tag(self, scope, key):
+        """
+        Get a user tag for the current course and the current user for a given key
+
+            scope: the current scope of the runtime
+            key: the key for the value we want
+        """
+        if scope != self.COURSE:
+            raise ValueError("unexpected scope {0}".format(scope))
+
+        return user_service.get_course_tag(self._get_current_user(),
+                                           self.runtime.course_id, key)
+
+    def set_tag(self, scope, key, value):
+        """
+        Set the user tag for the current course and the current user for a given key
+
+            scope: the current scope of the runtime
+            key: the key that to the value to be set
+            value: the value to set
+        """
+        if scope != self.COURSE:
+            raise ValueError("unexpected scope {0}".format(scope))
+
+        return user_service.set_course_tag(self._get_current_user(),
+                                           self.runtime.course_id, key, value)
+
+
 class LmsModuleSystem(LmsHandlerUrls, ModuleSystem):  # pylint: disable=abstract-method
     """
     ModuleSystem specialized to the LMS
     """
-    pass
+    def __init__(self, **kwargs):
+        services = kwargs.setdefault('services', {})
+        services['user_tags'] = UserTagsService(self)
+        services['partitions'] = LmsPartitionService(
+            user_tags_service=services['user_tags'],
+            course_id=kwargs.get('course_id', None),
+            track_function=kwargs.get('track_function', None),
+        )
+        super(LmsModuleSystem, self).__init__(**kwargs)
diff --git a/lms/lib/xblock/test/test_runtime.py b/lms/lib/xblock/test/test_runtime.py
index 63fd2fe763..0dbfe9c7ef 100644
--- a/lms/lib/xblock/test/test_runtime.py
+++ b/lms/lib/xblock/test/test_runtime.py
@@ -2,6 +2,7 @@
 Tests of the LMS XBlock Runtime and associated utilities
 """
 
+from django.contrib.auth.models import User
 from ddt import ddt, data
 from mock import Mock
 from unittest import TestCase
@@ -85,3 +86,43 @@ class TestHandlerUrl(TestCase):
     def test_handler_name(self):
         self.assertIn('handler1', self._parsed_path('handler1'))
         self.assertIn('handler_a', self._parsed_path('handler_a'))
+
+
+class TestUserServiceInterface(TestCase):
+
+    def setUp(self):
+        self.course_id = "org/course/run"
+
+        self.user = User(username='runtime_robot', email='runtime_robot@edx.org', password='test', first_name='Robot')
+        self.user.save()
+
+        def mock_get_real_user(_anon_id):
+            return self.user
+
+        self.runtime = LmsModuleSystem(
+            static_url='/static',
+            track_function=Mock(),
+            get_module=Mock(),
+            render_template=Mock(),
+            replace_urls=str,
+            course_id=self.course_id,
+            get_real_user=mock_get_real_user,
+            descriptor_runtime=Mock(),
+        )
+        self.scope = 'course'
+        self.key = 'key1'
+
+        self.mock_block = Mock()
+        self.mock_block.service_declaration.return_value = 'needs'
+
+    def test_get_set_tag(self):
+        # test for when we haven't set the tag yet
+        tag = self.runtime.service(self.mock_block, 'user_tags').get_tag(self.scope, self.key)
+        self.assertIsNone(tag)
+
+        # set the tag
+        set_value = 'value'
+        self.runtime.service(self.mock_block, 'user_tags').set_tag(self.scope, self.key, set_value)
+        tag = self.runtime.service(self.mock_block, 'user_tags').get_tag(self.scope, self.key)
+
+        self.assertEqual(tag, set_value)
diff --git a/lms/templates/split_test_staff_view.html b/lms/templates/split_test_staff_view.html
new file mode 100644
index 0000000000..bf65bd8921
--- /dev/null
+++ b/lms/templates/split_test_staff_view.html
@@ -0,0 +1,13 @@
+<div class="split-test-view">
+    <select class="split-test-select">
+        % for idx, item in enumerate(items):
+        <option value="${item['group_id']}">Group ${item['group_id']}</option>
+        %endfor
+    </select>
+
+    % for idx, item in enumerate(items):
+    <div class="split-test-child" data-group-id="${item['group_id']}"data-id="${item['id']}">
+        ${item['content']}
+    </div>
+    % endfor
+</div>
diff --git a/requirements/edx/base.txt b/requirements/edx/base.txt
index ec3914f563..1151120321 100644
--- a/requirements/edx/base.txt
+++ b/requirements/edx/base.txt
@@ -106,7 +106,7 @@ django-debug-toolbar-mongo
 # Used for testing
 chrono==1.0.2
 coverage==3.7
-ddt==0.7.0
+ddt==0.7.1
 django-crum==0.5
 django_nose==1.1
 factory_boy==2.2.1