I would suggest that something is really stressing him at school. Hitting teachers, now harming himself, would all seem to me to be signs of sensory overload. I would explore with the teachers exactly when these behaviors are occurring in the hopes of identifying and then mitigating the triggers. And don't accept any, "well he MUST learn" answers. If he can't handle something, he can't handle something, and the situation needs to be altered.
_________________
Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).