Suggestions needed.

My step - son started staying with us in November of last year. Since then he has had missing assignments, 0's on his grades and lately has been skipping class. He has skipped 2 classes between yesterday and today and has 5 skipped classes since he's moved here. He doesn't have a valid excuse for anything. His dad keeps talking but he keeps doing. Any suggestions on what steps to take next or what to do?.