Hello,
I instantly fell in love with the ponytail pulling! But I see how the composition is a bit linear. I think if the girl having her ponytail pulled were to turn her head around our way to look at the girl doing the pulling it will bring the flow back into the composition and make a sort of triangle with the 3 main girls.
I can't wait to see this in color!
EDIT: Oh, but I would hate to lose that wonderful "YANK" feeling!