My son, whom is now 16, has always done this. Right before his report card came out he had an average of 51 in English. All his other classes were A's and High B's. He made up the work and recieved a permenet grade of 85.
He gets punished if this happens and I ride him through the next grading period. I check his backpack for any papers and all his notebooks. I constantly email the teachers to make sure all assignments are turned in.
Then after we get through that grading period I try to let him do it on his own again. Sometimes he does right sometimes he doesn't.
Some boys are just this way. My daughter is not... she's quite the opposite.
Austin, my son, starts screaming that I don't trust him... but then I inform him that I would if he would do his work in the first place without me breathing down his neck. Also I don't allow any grade lower than 100% on Vocabulary or Spelling test because those are give me grades that you can study for a week before hand.
A. Lynn