My son has ADD and is on medication. He has always done badly in school. I've been doing everything I can to help, including taking away things, punishing him, working with counselors and teachers, and keeping track of his work. He just doesn't care about grades. He is failing everything except English. He isn't a troublemaker --- all his teachers say that he's a great kid. He just doesn't do the work. He is even neglecting his new braces. I'm at my wit's end!
There is a saying in counseling that if the client doesn't meet you halfway, then there will be no change. You say you have done everything, and that may be the problem. It's time for your son to do something. He is responsible for his grades. ADD is no excuse for failure. It appears that your son is choosing which courses he will pass. I would encourage you to focus on the fact that he is a good kid. Tell him that you appreciate his passing english, and that he is a good kid, but from now on he has to take responsibility for keeping track of his work. Tell him that you know he can do it for all subjects because he does it for english. Then, and this is the hardest part, let him pass or fail on his own. Set up the consequences -- summer school for failure or doing something special if he passes.
As for the braces, which are extremely expensive, I would take them away until he decides he really wants to put the time into taking care of them.