This is hard. The only thing you can really control is what kinds of foods are in the house, helping him to be active, and controlling adhd. Is he on meds? I’ve heard that is helpful when there is a impulsive eating going on as part of the larger impulse control issues.
I really wish school would stop all the food service (breakfast snacks, vending machines, party treats, fast food in the cafeteria, pizza delivery, etc). and focus on one nutritious hot lunch option.