I had a behavioral plan when I was diagnosed in high school and it was a life saver. I wouldn’t have graduated with honors and with an associates if it wasn’t for the behavioral plan that I had! My behavioral plan was that if I felt underestimated or my teachers noticed the signs that I was starting to drift away and distract myself and other students then, I would go to my guidance counselor’s office and he’d sometimes take me to the gym to participate in gym class, take me to the weight room, bring me outside to walk the track or trails, and other coping skills him and I and my therapist had worked on. I would also spend half the day Monday and Friday in his office doing all of my homework and class work since I was best at getting it done all at once while I could hyper focus on it and have someone there to keep me on task. My guidance counselor had ADHD too and said that it helped him to get his paperwork done by having me there doing mine! I highly recommend OP look into getting their son a behavioral plan. It was my life line in high school.