3.5... I love how this book breaks quite a few of the young Adult cliches, while still being a typical YA novel. I also love the main character, Sophie is great.
Also, I have a super-power, yes I am bragging, I can usually figure out the ending after the first round of hints--either I'm off my game or this book duped me (me = :) to be duped).
What the book lacked-- I just wanted more! More characterization more of the day to day school stuff- the teachers the classes- it just felt skated over- great world idea- little building on it. And the (very) ending pissed me off.