From my perspective, Ali, having had four kids go through high school ... by this time it's up to them. Yes, you can have house rules and not permit endless xbox playing etc., but you don't have to accept your son telling you it's your fault that he doesn't study well. It's HIS business to study now; it's his life that studying, or not studying, will affect. It's not your job to nag him - who will nag him in college? No one. He cannot lay this at your feet. Throw it back. Ask him what he wants out of life, what he thinks his life will look like in ten years and what he thinks it will take to get there.
Aside from self-starting his homework, he should be doing his own laundry by now and figuring out some decent cooking skills too. He could make dinner for the family once a week, for example. Not only will this allow him to survive with some reasonable health (and clean clothes) in college, it'll help you out and let him contribute to the family while he's still home.
