I have a son in the 4th grade and will not turn in his daily work nay suggestions?

My son will not turn in his daily work even though he can bring it home to finish in the afternoons. He does the work that he brings home and does it well but at school he does not complete it. He has lost his recess because of it and also been to after-school detention. I have taken the T.V., computer etc away nothing seems to work.