First, I’d have him screened for depression and learning disorders. It’s not uncommon for depression to hit just as the teenaged years do, and for learning disorders to be unrecognized and self-accommodated for in early years, and then begin to be a problem as higher level math is introduced. He may be struggling, and choose to be seen as “lazy” rather than “stupid” because it’s easier on the ego.
Next, I’d look at the school. Is it a new school? Is it a good school? A bad school can destroy a kid, and if that’s the problem, punishing him for it isn’t the answer, finding a better school (even if that’s homeschool) makes more sense.
If none of those are the problem, then (and I know already this is going to be unpopular advice), I’d let him fail if that’s what the school consequences are for his behavior. Better to fail in seventh grade than eighth, and better eighth than ninth, etc. The younger he is when he fails, the more surmountable that failure is (repeat a grade). If he isn’t allowed to fail until high school, you really risk him choosing to drop out when school isn’t compulsory.
People have this tendency to stop worrying about their problems if someone else will worry for them. If you show him that you’re emotionally involved with his grades, he knows you’re worrying about it, so he doesn’t have to. It’s your problem, not his.
Ultimately, his schoolwork is his responsibility. It might be hard, he might hate it, but it’s still his work and his choice. Your job as a parent is to provide a place, time and tools for doing his homework. His job is to do it. You may certainly say, “4-5:30 is homework time, not video game time. I’ll see you at 5:30 when homework time is done,” but if he wants to sit at the desk picking his nose for an hour and a half, that’s his call.
We tried riding our son at this stage, grounding him, taking away video games, finally literally sitting with him while he did his homework and checking it for him, and you know what he ended up doing? He’d do his homework, put it in his folder, put the folder in his bag and go to school…and then not turn in the homework. It was unbelievable. He’d still have missing assignments and low grades as a result, even though he’d done the homework. Most. Frustrating. Thing. Ever.
And, ultimately, what it taught him was that I thought he was an incompetent idiot who couldn’t think for himself. So that’s what he started acting like. I taught him that I loved his report card more than I loved him, and he honestly believed that.
Finally I told him something like, “I realized I’ve been stealing your homework from you. I’ve been treating it like it’s my job, and my worry, and that’s wrong. I’m sorry. It’s yours. I’m going to stop doing that. I’m now your coach. If you need my help, I’m here. If you ask, I’ll help. But I know that you can do it if you want to. I know you’re smart and capable of doing the work. Whether or not you do it is a matter between you and your teacher, and I’ll back her up with whatever the consequences are.”
Did it immediately improve his grades? Sort of. It took him two weeks to pull his F’s into better grades (in some cases, A’s!). The next year or so was good. Then there was another semester or so of him testing me, getting D’s and F’s and waiting for me to explode and punish him. I didn’t. I’d look over the report card, praise the A’s and B’s to high heaven, “huh” over the C’s, and ask him if he was happy with the D’s and F’s. When he’d say no, I’d ask him if he had a plan to deal with them. And that was it. When he finally realized that I was no longer “stealing” his work, no longer doing the worrying for him, he figured out that he’d better worry about it himself, and his grades quickly improved.
(Then he moved into a truly terrible high school and his grades nosedived for a couple of years until we could get him into a better one. I was always careful not to blame him for the grades he got while in a school which was truly hell. Now that he’s at a good school, he’s getting A’s and B’s again.)