Slingshot by Mercedes Helnwein

Grace Welles had resigned herself to the particular loneliness of being fifteen and stuck at a third-tier boarding school in the swamps of Florida, when she accidentally saves the new kid in her class from being beat up. With a single aim of a slingshot, the monotonous mathematics of her life are obliterated forever…because now there is this boy she never asked for. Wade Scholfield.

With Wade, Grace discovers a new way to exist. School rules are optional, life is bizarrely perfect, and conversations about wormholes can lead to make-out sessions that disrupt any logical stream of thoughts… Read more.