Saw Mean Girls, which 
is Tina Fey's dramatization of Rosalind Wiseman's
Queen Bees
and Wannabes. This is probably the best reason I've seen for 
small classes of similarly skilled kids. If tween kids are too different
in ability, some kids won't get worked and you'll get political behavior.
It's funny how this film pays homage to 
Chimpanzee
Politics.