diff --git a/src/spectator/dsl/builder.cr b/src/spectator/dsl/builder.cr
index 954bfc7..d1d4886 100644
--- a/src/spectator/dsl/builder.cr
+++ b/src/spectator/dsl/builder.cr
@@ -58,7 +58,7 @@ module Spectator
       end
 
       protected def build : ExampleGroup
-        root_group.build({} of Symbol => ValueWrapper)
+        root_group.build(nil, {} of Symbol => ValueWrapper)
       end
     end
   end
diff --git a/src/spectator/dsl/example_group_builder.cr b/src/spectator/dsl/example_group_builder.cr
index fda8402..f3814ce 100644
--- a/src/spectator/dsl/example_group_builder.cr
+++ b/src/spectator/dsl/example_group_builder.cr
@@ -1,7 +1,9 @@
 module Spectator
   module DSL
     class ExampleGroupBuilder
-      @children = [] of ExampleFactory | ExampleGroupBuilder
+      alias Child = ExampleFactory | ExampleGroupBuilder
+
+      @children = [] of Child
       @before_all_hooks = [] of ->
       @before_each_hooks = [] of ->
       @after_all_hooks = [] of ->
@@ -11,7 +13,7 @@ module Spectator
       def initialize(@what : String)
       end
 
-      def add_child(child : ExampleFactory | ExampleGroupBuilder) : Nil
+      def add_child(child : Child) : Nil
         @children << child
       end
 
@@ -35,8 +37,13 @@ module Spectator
         @around_each_hooks << block
       end
 
-      def build(locals : Hash(Symbol, ValueWrapper)) : ExampleGroup
-        raise NotImplementedError
+      def build(parent : ExampleGroup?, locals : Hash(Symbol, ValueWrapper)) : ExampleGroup
+        ExampleGroup.new(@what, parent).tap do |group|
+          children = @children.map do |child|
+            child.build(group, locals).as(ExampleGroup::Child)
+          end
+          group.children = children
+        end
       end
     end
   end
diff --git a/src/spectator/dsl/given_example_group_builder.cr b/src/spectator/dsl/given_example_group_builder.cr
index 5c6c4f9..7b53532 100644
--- a/src/spectator/dsl/given_example_group_builder.cr
+++ b/src/spectator/dsl/given_example_group_builder.cr
@@ -8,8 +8,18 @@ module Spectator
         super(what)
       end
 
-      def build(locals : Hash(Symbol, ValueWrapper)) : ExampleGroup
-        raise NotImplementedError
+      def build(parent : ExampleGroup?, locals : Hash(Symbol, ValueWrapper)) : ExampleGroup
+        ExampleGroup.new(@what, parent).tap do |group|
+          children = [] of ExampleGroup::Child
+          @collection.each do |value|
+            iter_locals = locals.merge({:TODO => value})
+            iter_children = @children.map do |child|
+              child.build(group, iter_locals)
+            end
+            children.concat(iter_children)
+          end
+          group.children = children
+        end
       end
     end
   end
diff --git a/src/spectator/example_group.cr b/src/spectator/example_group.cr
index 533f47c..154213d 100644
--- a/src/spectator/example_group.cr
+++ b/src/spectator/example_group.cr
@@ -2,47 +2,48 @@ require "./example"
 
 module Spectator
   class ExampleGroup
-    ROOT = ExampleGroup.new("ROOT")
+    alias Child = Example | ExampleGroup
 
     getter what : String
-    getter parent : ExampleGroup?
+
+    getter! parent : ExampleGroup
+
+    private getter! children : Array(Child)
+    setter children
+
     getter before_all_hooks = [] of ->
     getter before_each_hooks = [] of ->
     getter after_all_hooks = [] of ->
     getter after_each_hooks = [] of ->
     getter around_each_hooks = [] of Proc(Nil) ->
-    getter children = [] of ExampleFactory | ExampleGroup
 
     @before_all_hooks_run = false
     @after_all_hooks_run = false
 
-    def initialize(@what, @parent = nil)
-      if (parent = @parent)
-        parent.children << self
-      end
+    def initialize(@what, @parent)
     end
 
-    def examples : Enumerable(ExampleFactory)
-      @children.select { |child| child.is_a?(ExampleFactory) }.map { |child| child.unsafe_as(ExampleFactory) }
+    def examples : Enumerable(Example)
+      children.select { |child| child.is_a?(Example) }.map { |child| child.unsafe_as(Example) }
     end
 
     def groups : Enumerable(ExampleGroup)
-      @children.select { |child| child.is_a?(ExampleGroup) }.map { |child| child.unsafe_as(ExampleGroup) }
+      children.select { |child| child.is_a?(ExampleGroup) }.map { |child| child.unsafe_as(ExampleGroup) }
     end
 
     def example_count
-      @children.sum do |child|
-        child.is_a?(ExampleFactory) ? 1 : child.example_count
+      children.sum do |child|
+        child.is_a?(Example) ? 1 : child.example_count
       end
     end
 
-    def all_examples(locals = {} of Symbol => ValueWrapper)
+    def all_examples
       Array(Example).new(example_count).tap do |array|
-        @children.each do |child|
-          if child.is_a?(ExampleFactory)
-            array << child.build(locals)
+        children.each do |child|
+          if child.is_a?(Example)
+            array << child
           else
-            array.concat(child.all_examples(locals))
+            array.concat(child.all_examples)
           end
         end
       end