Avalon High, by Meg Cabot

Ellie is the new girl at Avalon High, but somehow everything seems very familiar. Will, the star quarterback and senior class president also has nagging a sense of déjà vu. As a series of bizarre events involving an ancient sword and a secret society bring them closer together, Ellie and Will begin to suspect the impossible. Could it be that the strange events unfolding at Avalon High also took place long ago…in the court of King Arthur?