Homework is needed to finish classwork.  We should think of homework as being a continuation of our classwork. Not everyone in the class works at the same rate so it is necessary for teachers to give anyone who is falling behind the chance to catch up. If this was done in class those who are faster would have nothing to do during this time, which would be a real waste of time. Homework then allows those who are behind to take as long as they need to catch up with the rest of the class.