On a normal weekend, Cheerilee assigns everypony an assignment from a unit she has been using for years. She considers it to be the most important one of the year; to teach the fillies and colts about the differences between ponies, and how they can all work together to do more than they could on their own. Unfortunately, a confused trip to the library by three fillies raises questions the teacher can't answer.

In an effort to make sure she teaches everything she can to the best of her ability, Cheerilee enlists the aid of Twilight Sparkle to help rewrite the textbook she has been using for years. As the days tick by, however, she is forced to deal with something she thought she had a handle on a long time ago.