I have twin 14 yo boys who turn 15 next summer and my first thought is that he's in the wrong grade. I have a boy in 9th and a boy in 10th (who skipped). I'm wondering if the academic work is just not challenging enough for him to rise to the occasion? My 9th grader is really frustrated with school right now because he thinks everything except his two honors classes are too easy. (He should have skipped, too.) But he would go bonkers if he were in 8th grade. So I'm wondering if your son just doesn't think the work is worth his effort? Can you talk to him and the school about the academic challenge and see if there's anything that can be addressed?
He had to be 5 by Aug 1st to start Kindergarten, and he has a late Aug. birthday, so that's the reason why he seems older. He is honors level classes, so he's definitely challenged and based on maturity, he's right where he needs to be. 
Besides looking at the academic challenge, I would also have dinner time conversations about your values ("do your best" being one of them), the importance of grit and a growth mindset. I think there's a growth mindset book for kids that also might help. Find out how he feels about his study habits and grades, and find out what his goals are and ask where he needs your help.
I think you're right about having your son own his academics. Our attitude is that our kids' job is school, which needs to be their first priority and everything else is a privilege. I would not be OK with forgotten homework and assignments, especially if it got worse instead of better over the years. So in your case, I would take a carrot and stick approach. Sounds like he's not truthful all the time about turning in assignments. What's the consequence for that? For my son, he would lose games and his phone for a week. If he got a C, sorry to say, he wouldn't get to game until his grade was at least a B. It's one thing to study and get a C. That's a bummer, and we can look at what went wrong and learn from it. But to not study, and not do all the work and get a C? I would take a hard line and not be sympathetic when he lost privileges until the next grading period.
I'm with you on this. How do you handle it practically? DS's teachers all put grades in, in a different time period. Some are updated quickly, some not for weeks...very frustrating. I really want to implement this. I think a week is very fair, but still would keep him motivated. I'm the same way, if you study hard and still get a C, back to the drawing board, but a C due to lazy work, no way.At the same time, I would probably also reward him for good study habits and grades. I don't actually do that for my kids, but if they were having trouble getting motivated, I wouldn't have a problem finding external motivation for a while. Is there something he wants to work toward that he could earn with good grades? (A skateboard, a trip, a gadget, etc.) In my view, he creates good work habits as he's earning the good grade, and he doesn't lose that when the reward ends.
Great idea!!I'm not saying my boys haven't ever struggled with motivation-- they have! They're not having the issue right now-- who knows, it might happen again!
Good luck. I always think it's best to be proactive, and it sounds like you are.
P.S. One of my boys did accutane, too. (Early puberty!) I know it gave him some fatigue, but it wasn't enough to affect school or his competitive sport. I seriously doubt it's a factor in what's going on with your son.
