My son is very non-compliant at school. It's so bad that he's about to get kicked out of Pre-K. Like you our rules are very firm at our house. He knows what he is and isn't allowed to do. Unfortunately doing whatever it is that he wants outweighs the punishment later.
At home if I give him something challenging to do he will focus on it and sit somewhat still longer than normal so maybe it's like what everybody else has said. Maybe he's not being challenged enough and it's causing him to act like that.
My son's teacher told him that if he didn't behave he wouldn't be allowed to stay in Pre-K. He told her that that was fine because there wasn't anything that she was teaching that he didn't know. We don't tolerate sassy remarks like that at home but that might give you an example of what his school has to deal with. Sounds like your son might be a little of the same way.
Have they tried challenging him at all to see if it helps?
