Another idea is to market to teachers. Scan in homework, grade/annotate on the computer, and send results to student and parents. Then, teachers wouldn't have to lug all that paper around, parents are involved in the feedback loop, 9 month sales window, doesn't require institutional commitments (any teacher could use it).
I would pay for that! The amount of paper that my kids bring home from school every day is staggering. If I could go online and see scans of all their work (along with all the school newsletters, PTO flyers, lunch menus, etc.) that would be wonderful. Of course you'd need to figure out how to make it easy for the teacher to scan/upload of stacks of different sized, often folded/wrinkled paper.
Actually figuring out how to scan papers would be the hardest part. I think it would require an affiliate deal with a document scanner company. Or perhaps they're cheap enough that you could give away document scanners for a year's subscription (say $120 a year plus a free $60 doc scanner).