What is the best approach you’ve found to help when dealing with parents who are not involved, no matter what the situation may be?

To touch on this, I have a student this semester who shows no interest in anything at all. Whether it's an individual assignment, a group assignment, or a hands-on activity, he doesn't care to participate. Add in that he will talk to anyone he can get to engage in conversation with him, and it feels like I'm fighting a losing battle. I've had the one-on-one conversations, done the guidance referrals, called home, and nothing changes. The parent he lives with basically said he's not their problem; all they have to do is drop him off and pick him up at the correct time.

While my heart breaks for this student, I also can't justify being okay with him moving on to the next grade level. Aside from the work issue, he might come to school 2 days, then be out for 5-7. Any ideas?