I think the downfall of most high-school type RPs are the following:

1) too much focus on romance
2) not enough focus on a plot driven storyline
3) players writing their characters as actual high school students



The third point seems counter intuitive but it's true. A high school based [i]movie[/i] is appealing to a wide audience when your actors come across as being mature and older than actual high schoolers. Let's be honest - 15 yr old students in real life are kinda boring and silly.

Write your students as mature, write them as people and not horny animals, and stay focused on a plot and you should have a decent RP.