diff --git a/Gemfile b/Gemfile
index 209c342a..e287d5a8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -26,6 +26,9 @@ gem 'gravatar_image_tag',              '~> 1.2'
 gem 'inline_svg',                      '~> 1.3', '>= 1.3.1'
 gem 'faker',                           '~> 1.8', '>= 1.8.7'
 
+# Used for bulk inserting data into database using ActiveRecord.
+gem 'activerecord-import',             '~> 0.23.0'
+
 # Used to round time to the nearest hour.
 gem 'rounding',                        '~> 1.0', '>= 1.0.1'
 
diff --git a/Gemfile.lock b/Gemfile.lock
index 12ebe00b..1e033049 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -33,6 +33,8 @@ GEM
       activemodel (= 5.1.6)
       activesupport (= 5.1.6)
       arel (~> 8.0)
+    activerecord-import (0.23.0)
+      activerecord (>= 3.2)
     activesupport (5.1.6)
       concurrent-ruby (~> 1.0, >= 1.0.2)
       i18n (>= 0.7, < 2)
@@ -374,6 +376,7 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
+  activerecord-import (~> 0.23.0)
   bcrypt (~> 3.1.7)
   bootstrap (~> 4.0.0.beta2.1)
   bootstrap-will_paginate (= 1.0.0)
diff --git a/app/models/sample_event.rb b/app/models/sample_event.rb
index dff44530..3764f30b 100644
--- a/app/models/sample_event.rb
+++ b/app/models/sample_event.rb
@@ -8,6 +8,7 @@ def self.build_for_group(group)
   def initialize(group)
     @group = group
     @event = nil
+    @attendances = []
   end
 
   def build_sample_event
@@ -69,10 +70,15 @@ def event_address
     end
 
     def add_sample_attendees
-      random_members = group.members_with_role.shuffle[0..29]
-
       random_members.each do |member|
-        @event.attendees << member
+        @attendances << Attendance.new(
+          attendee: member, attended_event: @event)
       end
+
+      Attendance.import(@attendances)
+    end
+
+    def random_members
+      group.members_with_role.shuffle[0..29]
     end
 end
diff --git a/app/models/sample_group.rb b/app/models/sample_group.rb
index 150cedf1..3e995fde 100644
--- a/app/models/sample_group.rb
+++ b/app/models/sample_group.rb
@@ -8,6 +8,7 @@ def self.create_for_user(user)
   def initialize(user)
     @user  = user
     @group = nil
+    @memberships = []
   end
 
   def create_sample_group
@@ -47,9 +48,24 @@ def group_location
     end
 
     def add_sample_members
+      create_memberships
+      add_member_role_to_memberships
+    end
+
+    # We are using 'activerecord-import' for bulk inserting the data.
+    # https://github.com/zdennis/activerecord-import/wiki/Examples
+    def create_memberships
       SampleUser.all.each do |user|
-        group.members << user
-        user.add_role :member, group
+        @memberships << GroupMembership.new(group: @group, user: user)
+      end
+
+      GroupMembership.import(@memberships)
+    end
+
+    def add_member_role_to_memberships
+      # https://github.com/zdennis/activerecord-import/wiki/Callbacks
+      @memberships.each do |membership|
+        membership.run_callbacks(:save) { false }
       end
     end
 
diff --git a/test/models/sample_event_test.rb b/test/models/sample_event_test.rb
index bdc00a57..020933d0 100644
--- a/test/models/sample_event_test.rb
+++ b/test/models/sample_event_test.rb
@@ -3,14 +3,24 @@
 class SampleEventTest < ActiveSupport::TestCase
   def setup
     stub_geocoder
+    @group = Group.last
   end
 
   test "creates event with sample attendees" do
-    group = Group.last
-    SampleEvent.build_for_group(group)
+    add_members_with_role
+
+    SampleEvent.build_for_group(@group)
     event = Event.last
 
-    assert event.organizer, group.owner
-    assert event.attendees, group.members
+    assert_equal event.organizer, @group.owner
+    assert_equal event.attendees, @group.members
   end
+
+  private
+
+    def add_members_with_role
+      @group.members.each do |user|
+        user.add_role :member, @group
+      end
+    end
 end
diff --git a/test/models/sample_group_test.rb b/test/models/sample_group_test.rb
index 67431c97..a5b899c2 100644
--- a/test/models/sample_group_test.rb
+++ b/test/models/sample_group_test.rb
@@ -1,18 +1,28 @@
 require 'test_helper'
 
 class SampleGroupTest < ActiveSupport::TestCase
+  GROUP_OWNER_COUNT = 1
+
   def setup
     stub_geocoder
   end
 
   test "creates group with sample members, organizer and event" do
     user = users(:stranger)
+
     SampleGroup.create_for_user(user)
     group = Group.last
 
+    members_count = SampleUser.all.count
+    organizers_count = group.organizers.count - GROUP_OWNER_COUNT
+    members_with_role_count = members_count - organizers_count
+
     assert group.sample_group?
     assert_equal user, group.owner
-    assert SampleUser.all.count, group.members.count
+
+    assert_equal SampleUser.all, group.members
+    assert_equal members_with_role_count, group.members_with_role.count
+
     assert_equal 5, group.organizers.count
     assert_equal 1, group.events.count
   end