I don't see dragging the police into the situation as a means to an end, but I would let the principal know that if something wasn't done to remedy the situation and punish the little snot that you next course if action will be getting the authorities involved. No cbild should have to fear other kids in school and no parent should have to worry that their children are in harms way while being there. The school needs to treat every student fairly and equally. If the principal doesn't want to take appropriate corrective action, get the authorities involved.