It is sad. However I really feel you do not have a leg to stand on. In private schools they can tell you how to look, and even in some public schools as well. You need to look at the dress code for the school and see what it has to say. If there is a part about hair and apearence you are probally out of luck. If it is not so specific and is written that you cannot be a disruptive influence have them prove to you that you are one. No matter what you have a long fight in front of you.