I know this is hard especially if you work all day. But think of it this way, the child goes to school all day long, then has to come home and do homework - it just doesn't seem fair, does it?
Sit with your child at the kitchen table while he does his homework. You could take a class and do your work at the same time, or catch up on household paperwork. But stay with him and make sure he gets it done.
No, grounding doesn't work. My daughter's husband spent most of high school grounded due to grades and their punishment never accomplished anything but resentment.
Check his homework when it is done and praise him when he gets good grades and maybe a small reward.