Ask the school counselor to observe your son in the classroom so that you can have an objective opinion of what is going on there. Find out exactly what he is doing in class that is causing problems so that you'll know what he needs to work on. Talk with both the teacher and the counselor and come up with a plan to help your son with his behavior.
Pick one or two behaviors to improve first (staying in his seat, for example). Ask the teacher to focus on those behaviors and to positively reinforce your son when he is behaving appropriately, giving him praise and a sticker when he sits in his seat for an activity.
The teacher can let you know daily how your son's behavior was and you can follow up at home. A good day can earn an extra bedtime story or a walk outside just with you; two or three good days in a week can earn having a friend over to play on the weekend. The key to a system like this is to do it consistently over a long period of time, increasing the level of behavior required to earn a reward as his behavior improves.
The counselor may be able to give your son some individual time or include him in a small group on good behavior. You may also want to pursue family counseling outside the school to help you and your husband be better able to deal with your son and his ability to "push your buttons." The counselor or your pediatrician can refer you to a therapist in your community who can help.