When students don't turn in homework, they are given a homework card. On this card, they write their name, date, assignment and the reason they did not complete it. Every grading period they may get up to three cards. On the fourth card, they get a letter home with a copy of the card attached requiring their parents' signature. Just knowing that the parents are going to see the excuses does the trick every time. In the extreme case that even the letter doesn't change things, the student has to call the parent when they don't turn in the homework.