It's not a great territory for startups, because the buying decisions are made by such bureaucratic organizations. There's no group of clever, poor early adopters for a startup to start with.
But maybe the idea can appeal to the growing nontraditional markets: tutoring, distance education, self-education, corporate training, for-profit higher-ed (U of Phoenix, ITT, etc.).
Also: internet in the schools brings advertising at a level far beyond the controversies that affected ChannelOne/Edison in the 90s. Not all school computers have ad blockers, do they? So perhaps even an ad-supported model would work for a really lean educational web-app startup -- and there's little more lean than a single teen founder.
I had a website that I was selling advanced CBT on it, like PHP, C, cisco, perl training videos, and it was doing very good. I had to stop it because the items that I was selling were illegal, and this was the only reason. :)