There is no single reason why children hit their head or bang against something. Generally it occurs because the child is very frustrated and does not maintain emotional control. The behavior at school would improve if the school adopted a plan whereby they discipline (or reward) him at school and not remove him. In fact, the current plan may well be exacerbating, not helping, the situation.
Thank you for your response. We do have a plan with the school and we do exactly what you suggested above. It doesn't seem to help though. He has the I don't care attitude about so many things. I would really like to know why he is so bad there and not at home. It bother's me that anytime he acts out the school sends him home immediatly and doesn't deal with the behavior as it occurs. I would also really like to know why he hits and bangs his head against things.
There should be a plan whereby you and the school collaborate to address your son's behavior. For example, each day you can be informed of whether or not your son has adhered to the code of conduct of the school. If so, he can have access to his video games (or whatever activity he prefers). If he has not followed the school rules, he would be denied access to the game/activity for that day. Do you see what i am getting at? Hopefully the motivation to have access to his pursuits at home will enhance his self-control at work.
You might also re-visit the ADHD issue. perhaps it is more of a problem than you think. Children do notoutgrow ADHD - it is a persistent condition. Now what can occur as children get older is a greater capacity to control their behavior. The ADHD condition remains, but it may have less of an influence.