Send a complaint letter to their management and describe about the attitude of this teacher. Keep sending it and if still no action been taken. The final act is try to find other few concern parents and go to the press, report to them about this incident. They realy love this kind of story to be advert in their newspaper.This is about the reputation of the school. I think the school management will take serious action once it goes to the newspaper coz those reporters will send them a visit hehe