Unfortunately, I found that my teen son needed more direct homeschool supervision than I would have liked<g>. It does get better, I promise. Just hang in there. I personally feel that keeping him involved socially with friends is quite important.
It might not be fun, you may have to spend a lot of time proactively monitoring his school since waiting for the zero is a no win situation. Perhaps over the weekend, you and he can come up with a chart of assignments for the week? And if he is doing assignments on the computer you may have to sit where you can see the screen to make sure his is not getting off task.
Boys, especially, but all teens, sometimes, need extra help to stay organized and stay on task.:)