Since you’re asking the question, I think you know deep down that you are enabling him. The traditional “tough love” approach however, doesn’t work. I think he has stopped trying because he doesn’t believe that he can succeed. Pep talks are not enough; he can’t make himself believe the speeches because everything that he has experienced for his whole life has proved to him that he is not like everyone else. He knows for a fact that there are some barriers, and the traditional “try harder” approach just doesn’t work. Since he doesn’t know what else to do, he has given up.
The way most class rooms are set up is difficult for people with ADHD; if his home life was also unstructured its no wonder he had difficulty. Bad marks are one thing, but when a child realizes that his own parents don’t expect anything from him, it is impossible to have a healthy self-esteem. Don’t believe me? Try giving him 2 minutes to write down all his strengths and 30 seconds to write down his weaknesses. I guarantee the weakness list will be longer. To quote Dr Annick Vincent: “you know the cure for low self-esteem? Success!”
I would suggest using his computer skills to his advantage. A quick google search of “online K-12” found several internet high schools: here is one: https://www.k12.com/virtual-school-offerings/high-school.htm. Online learning is much easier than classroom learning, at least it is for someone with ADHD. The thing is- ADHD is not really a disability, it’s just a difference. Our brains work differently and self-directed education plays to our strengths. I think he will be surprised at how well he does. I think he will discover that he is smarter than he ever thought he was.
The boost to his confidence may make him want to learn more about his ADHD and how work smarter- not harder. This web site has many articles and webinars that are helpful. I would also recommend TotallyADD.com. In the end, it’s his brain and his life- only he can figure out how to use it to get the life he wants.