Hi... a really able child can have just as many problems at school than one who is struggling. It is the school's responsibility to work out strategies that work for your son. You are right ro be concerned and do need ensure that the school nips this in the bud. I would suggest posiitive enforcement of good behaviour etc. Tell them what works for your child.
If you do not get anywhere with the class teacher (most teachers are excellent but sometimes a particular teacher is not great wih a particular type of child), I suggest you make an appointment with the head, or the senco and express your concerns and try to devise a way forward. You seem like a very sensible and caring mum who knows how to manage your child. It sounds to me like you are doing your job and the school just hasn't managed to find the way that works for your son.
I like the reward idea. I know of other strategies.... like marbles in jars.... they go in for good behaviour, out for bad.... and if it's full at the end of the week (or day... whatever) a reward is given. Home -school books can be used..... ummm can't think of anymore off the top of my head!!!