My daughter's school has always had that rule. I'm fine with it - if the school's dress code says no skirts that short, why should the cheer uniform be an exception? They can still wear it, just with sweatpants underneath. People already think football players and cheerleaders get all the special treatment (while we may think this is not true, it is a perception a lot of people have about cheerleading). I'm a firm believer in rules applying to everyone equally across the board.
Be glad that's all they're doing. Last year when the cheerleaders tried to fight the sweatpants rule based on the fact that the cheer uni was school-issued, the principal suggested that they change the uniform to meet the school's dress code!!! :eek: That shut the girls up quick.