You guys could even get double the amount of streaming in funds from ad revenue related to studying. (I wouldn't want ads on clash of clans or something)
And to get an almost garanteed donation, you can have a subscription for an ad-free variet of the application, for something like $1 a month. $1 x 6000 students, every month, for every year.
That sounds pretty good to me.
However, if you want more people considering the app over the free and easily accessible web version, you have to add some more perks to the app version exclusively so it could be more enticing. (This part is up to you and suggestions taken from the website users). I would suggest a ranking leaderboard system. You already have one for 'the most commented, most liked, most files', but one with 'top 100 influential' would definitely be great. It would be hard to make leaders over messages, but if you guys manage to find a way to represent that on a leaderboard, that would be AWESOME!