R.Y.
I am not ADD but I definitely have days when I am disorganized and have trouble focusing...and days when I yell or feel like yelling. If your son can understand enough to say you can yell but I will still do what I want...then he can understand he has a choice about how he behaves (even if some things are a little harder for him because of the ADD). The trick is to give him positive reinforcement for good behavior and negative consequences for poor behavior. Try and pick one or two behaviors to change at a time and think of consequences ahead of time.
Also, if he has trouble sitting still for academic work maybe you can think of ways to alternate the work with active breaks like jumping on a mini trampoline. Or maybe you can help him match some of what he is learning with a motion or action(like making the shape of a letter with his arm or hand--I think Waldorf schools have a whole system for this)