Rarity, Pinkie Pie, and Cheerilee have been hinted as long time (or life time) residents of Ponyville. So I imagine they all went to the same schools together. So here they are probably in their last year of school before graduation (well for Rarity and Cheerilee at least) as school cheerleaders (I guess for hoofball). That is my story anyway, really I wanted to do something silly and have an excuse for "Eighties Cheerilee" to be doing something. Of Course Pinkie cheers with the most enthusiasm, and Rarity well she can never get entirely used to Pinkie's style (Cheerilee seems cool with it though).