My two cents, (well 1.537 after exchange) is play them with the "take back rule". I taught my daughter chess this way. If you see him about to make a mistake, tactics or strategy wise, ask them if that is a wise move. Don't tell them not to, just ask them. Give them a second to see if they can see what you are seeing. This does two things. A) lets you gauge how they are doing, (my daughter quickly started seeing things I didn't.... I no longer play chess with her), and 2) it will help with cognitive abilities. If they don't see it, point out what you see. They will then keep an eye out for that, (mimicry and all), but, the way a youths mind leaps, they will start to see other stuff. He may need help tracking everything he has, so, give him all the time he needs on his turns without pressuring him. In the end I think he will love it. Then, when he makes the nationals and worlds you can quietly gloat in the corner.
Edit, sorry if this comes off a bit preachy. Not my intent. I blame the ADHD
Not at all. This, (along with the other posts) is good advice.