Speak by Laurie Halse Anderson (1999)

Melinda Sordino starts the school year as an outcast. Her friends won't talk to her, because at the end of the summer she called the police at a party and got everyone busted. What her friends don't know, however, is why she called the police. Nor do her parents, or anyone else for that matter. Because Melinda is saying as little as possible this year. An emotional and redemptive (but also dryly funny) novel and spot on in its depiction of high school life.