But the moment you call it a startup, I have to ask how you make money. So, how do you plan to make money? Students are poor, and cheap, and I'm not sure ads would fit it even if you had the traffic.
It also makes the thing actually useful for me -- I don't want to have to remember to add the assignments to it myself. I already know what my assignments are and I don't have time to type them into yet another place.
For study notes, I think an Amazon affiliate model would probably work best. Ebay would be tempting (i.e. potentially cheaper) but likely to throw up less relevant results.
As for packaging up and selling to schools - great, but even greater would be to provide schools with their own hosted version instead. They set up a CNAME off their domain pointed at a hosted version and students can work within their own schools. This would also work for colleges.