I went through that with my boy. It started his freshman year, too. He got all A's in class, but never did the homework. When he did it was worth 1/2 or 1/4 credit. Which would always put him in the C's & D's grades.
I put together an assignment sheet that had to be signed daily from each teacher for every class he had and he had to bring his homework home for me too, so that I knew it was done. That lasted a few months, then he was doing better on his own writing down his assignments.
If everything was turned in he could go out that weekend. Otherwise he was grounded.
It was sophmore year that he really got things in gear. He wanted to get his driver's license so bad, that he did whatever it took to get them. He made A's across the board.
Junior year, he started slacking off again. The teachers all knew he could do, and he did do his assignments, he just forgot to turn them in.
Senior year, he got some things turned in, the missing assignments caught up to him. He almost didn't graduate. he had to take an extra class to get caught up, but he did graduate with his class.
Now, he's turning 21 this May, and starting college.
I can share with you one thing I've learned, there's our time & then there is God's time. Every child is different and unique. I wasn't about to scream and hollar at him because he didn't get his work done. I knew he was a bright child. And I also knew he could do what ever he wanted if he chose to. Well after high school he had some odd ball jobs, and he's 21 and not making the kind of money that he wants. Sometimes learning on their own is the only way they are going to learn. Now he's making life changes. And I know he's going to great, because he doesn't want to go back to what he was doing.
If your son is talented with music then that is his calling. There are so many people in this world that were horrible in school, like Albert Einstein, to name one. But look who he turned out to be. Your son is just destined for greater things! Sounds like he's an impressive young man! Congratulations!!