Hex Hall by Rachel Hawkins

Sophie Mercer is just like any other high school girl, except you know, she's a WITCH. Three years ago Sophie discovered that she actually has magical powers and is trying to keep them under control - which she fails at miserably.

Now she's being sent into a school for wayward Prodigium, a.k.a. witches, faeries, and shapeshifters. Hecate Hall or Hex Hall is an isolated reform school which is pretty much a more hellish version of highschool. Beautiful girls still rule but now they have magical powers in their side. There's the weird roommate but she also happens to be a vampire. And of course, the hot guy who kicks your ass in class because you can't seem to get a hang of your powers.

However, a series of chilling failed murders get Sophie's attention and she's pulled into a world that no prodigium must be in.