Is it possible that he has ADD? Is he easily distracted? Does he fidget? Can he not focus on what he’s doing? If so, he may need to address this with his doctor. There are treatments that can help him improve in those areas. If that doesn’t seem to apply, I can’t think of any better advice than what you’ve already given him, but I do have some advice for you. You need to remember that while you’d like to see him succeed, it’s not worth fighting about. He is your friend, he may never get any better at this, and that’s ok. Just support him.