is the teacher male or female , and does it make a difference in your eyes OP?
I think it is perfectly reasonable for the school to suggest this. Cuts down on silly comments from some of the boys, prevents girls being so self conscious leaving them free to have their fun. Maybe the staff know something the parents don't about eg the man who lives opposite and likes to watch the little girls?
And I am sure there are schools who ban cartwheels and handstands for health and safety reasons, so at least yours is better than that!