Eco, I just finished
The Learning Habit last week, and one point it makes is that it distinguishes between creative screen time and consumer screen time, and that kids tend to binge excessively on consumer screen time, not creative screen time. (No one stays up all night making Powerpoints - at least not for fun.) It sounds like he is doing a fair amount of creative screen time, and I'd avoid taking that away.
I like DeeDee's idea of the bright tape flags. If you can find enough colors, I'd do it like this:
Each class has a color. Finished homework gets a tape flag of the appropriate color. If a class has no homework to turn in, a tape flag of that class' color goes on the front of the planner (or a designated page inside if they tend to fall off the front). As he turns homework in, he is to take the tape flag off and put it on the front of his planner. At the end of the day, if he doesn't have a flag of every color on his planner, he should look for missing homework assignments to turn them in (he can do this while he is getting his planner initialed).
Places where this could fall apart - he forgets to take the tape flags back off his homework, he (or you, at the start) forgets to "reset" the flags at the start of the day, he forgets to look for the tape flags at the end of the day. Possible solutions - he could ask the teachers if he left the tape flag on his homework when he goes to get their initials at the end of the day, you could set some kind of timer in the evenings to do the "reset" for he next day, you could arrange for his study hall teacher to help/remind him to check his flags.
One system worth looking at is
HOPS - it's a very structured school-based intervention aimed at disorganized middle school kids, one that is supported by research. If you could get the school to implement it, that would be great. Even reading what it says about the order of steps and how long it takes to implement would be an improvement.
Good luck!
