That’s Not What I Heard, by Stephanie Kate Strohm
When two high school seniors break up accidentally, the entire school is thrown into mayhem. A single rumor that’s… err, well… almost true takes on a life of its own until half the school won’t even speak to the other half, the teachers are all taking sides, and two of the most responsible students in the district are kicking up more trouble in a single week (without even trying) than most people manage in a lifetime.