Try Your Worst by Chatham Greenfield

Sadie Katz and Cleo Chapman have been rivals since birth, when they competed to be the first baby born in the new year, and Cleo has won almost every contest since. In senior year in St. Augustine, Florida, they are neck and neck for valedictorian when a string of escalating pranks at school, from slashed tires to locker graffiti, is pinned on them, and the principal threatens to tell their colleges. Facing expulsion, they team up to find who is framing them. As they investigate, Sadie questions her Ivy League plans, Cleo wonders whether to stop settling for what comes easily, and both begin to see the rivalry differently.