Wait, didn't you post that you could see why a small boy could be teased for an earring??? I know I'm in a conservative area, but I would think a young boy in a skirt or dress would REALLY be teased in most places of the US. I assume that's why they have the rule--to prevent class disruption, not to deny someone an experience.
It doesn't matter to me since I figure my kids can wear whatever they want the other 16+ hrs of the day.
If they want to prevent class disruptions they can actually do something about kids teasing each other instead of putting on the person being teased to conform.