Hello and Thank You for using Just Answer. I am sorry to hear about your son's problems in his new school setting. Since you already have a reward system set up, then maybe you should try role playing techniques. Your son needs to be taught how to behave in certain situatins before they actually occur. So what you need to do is take on the role of one of the instigating students or set up a situation in which your son would over react. Your son plays "himself". At out a scene with you taking the lead. See how he would react and then explain to him the proper behavior and the reason for the correct behavior. You may need to do this several times with many different scenarios until it becomes very natural for him to act better. Hope this helps!!! Have a great day!!!!
Oh , also make sure the teachers have a reward system set up at school as well.