E.J.
I assume this is a private school, so my thoughts are kind of based on a public school, but here it goes. Many schools are going to full inclusion of individuals identified with disabilities, so I feel it is a disservice to other child to kick him out of school or assume that he belongs in special needs school. However, it is not okay that he is hurting your child. The school needs to have a plan to deal with this behavior. The school is only reinforcing the behavior by tip toeing around it. Also, by not getting any sort of consequence the child's behavior is being reinforced, hence the recurring incidents of scratching. The other children have a right to a safe education and they should not have to suck it up and accept that he is putting his hands on them. They are doing the boy a disservice by not implementing a behavior plan that would teach him better skills to cope with whatever is causing him to do this. After all, the real world won't tip toe around him.
I think you absolutely should address this with the director, but go in cool and collected. Being emotional (which is hard b/c you are emotionally attached to the situation) will not help. Even if you have to take notes with you, objectively state how this is not right that your child is being injured at school. Express your concerns and express that you feel the school must do something to make it a safe environment for all the children there. Maybe bringing it to the directors attention well help the school bring in professionals or some training in this area. Maybe the teacher just doesn't know what to do about it.
I don't know anything about the mother, so I can't make assumptions. I'm not bashing any teachers b/c I will be one myself. I am a mother of a special needs boy who has an Autism diagnosis. I see him struggling in social situations and resorting to hitting etc. The teacher has not said one word to me and I personally initiated a meeting which I am going to today. I want to set a clear behavior plan. My son told me that he doesn't get in trouble b/c the teacher does not see him. Even though the school has not expressed any concern I am expressing concern. I do not want his behavior reinforced b/c the teacher is not seeing it or doing anything. I want a plan that implements reinforcing positive behavior and a discussion of a plan that can help us all teach him appropriate social skills. So... I find it sad if the mother did not inform the school that there were things going on, but they need to find a solution to the problem.
I hope all goes well and that you can discuss this with the school in a manner which can help all the students be successful and most importantly safe.