I’m a HS teacher (24 yrs) and coach at one of the more competitive athletic schools in my state – and I have ADD. If it’s a traditional ‘line-style’ drill, one way would be to make sure that after the coach has explained the drill he’s 3rd or 4th in line, and watch the first few players closely and mirror what they do. I say 3-4 back because any further back and he may lose his concentration/focus on the drill; also, he’ll have to stay focused because his turn will come quickly enough! Drills are really about building skills, so his place in line should have no bearing on his ability/standing on the team.
Another way would also be for your son to talk to his coach. If the coach is a real professional, he/she will want to work with one of their players to make sure they maximize their players’ potential for the good of the team. No need to mention ADD (unless you’re comfortable doing so), but just for him to say he’s having a hard time focusing on some of the instructions re: drills, and what can be done to help that. Maybe it’s because of my own ADD, but I would respect the courage and insight of S player who’s asking in order to get better. I hope this helps…