I read The Mockingbirds, by Daisy Whitney, with book club a couple of years ago and liked it. It's about an exclusive private boarding school whose administrators trust the students to always behave honorably. Well, we know that's an ambitious / unrealistic hope! So for those times when they don't, there is a secret society of students dedicated to righting the wrongs of their classmates, since the administrators won't do it for them. This book deals with date rape, so I would say it's better for 11th- and 12th-graders. It was well written, well thought out, and I liked the way she dealt out the details.
Anarda sent the sequel, called The Rivals, home in my book bag a couple of weeks ago. (She often sneaks books in there with little notes saying "READ ME!") So I read it.