C.S.
Hi T.,
My son was doing the exact same thing and organization was a large part of the problem. I purchased a folder (one of the plastic ones) that was for turn-in homework only. Each night as he would complete his homework I would ask him if he put it in his "turn-in" folder. Each side of the folder was for a teacher (he only had two teachers last year).
Then the second part of the problem was laziness/irresponsibility, so I came up with a system and made a deal with him. The system was that each evening I would go through the agenda and write the assignments on a 3x5 card. I would leave a space next to each one for initials. Each day as he had those subjects he had to get the teachers to initial next to the assignments as he turned them in. At the end of the day he gave me the card. At the end of the week if he had turned in everything he got a reward. His reward was that he got to go to the ceramic studio on Friday evening and paint an item. You could use whatever reward you want, but it should be something worth working for...I normally try to pick something I would do any way, but they don't have to know that! ;-)
We all know that positive reinforcement works better than negative punishment (I am not opposed to punishment when it is called for), but positive reinforcement gets the work done, and also makes the child feel a sense of pride and accomplishment! Make sure you follow through on the reward promised (rent a movie, rent a video game, pizza night, whatever) and make sure the reward is worth working for! Let them choose at the beginning of the week so he knows what he is working for. Put a chart up or mark stars on the calendar. It doesn't have to be a huge production, but just make sure your reinforce it.
What I figured out with my son is that he did not care about grades, so I had to find a currency he would work for. No one wants to go to work for free every day, we work for a pay check. This year he is in 6th grade and has a facination with caviar for some reason -- I think he read about it in a book. So, our deal is that he gets honor roll and I buy him some caviar to try. I figure it is worth me not having to do the 3x5 card every day since I want him to learn to manage without me. We shall see! ;-)
Good luck!