The school for wicked witches

In Oz, most girls and boys with magical powers are sent from the north, south, east, and west to renowned witch academies, where they are elevated and taught all the finer ways to be a responsible witch. But if you misbehave? Or are thought to harbor darker magic? You're sent to the equivalent of witch reform school -- The School for Wicked Witches. ONLY! Once you get there, you find that the witches running it are so powerful that they've managed to trick the rest of the outside world. Yes, it looks to outside like they are taming the wickedness out of the witches... but in truth, the school is run by wicked witches (who, incidentally, don't see themselves as wicked at all... although some of them really are.)

Ava Heartstraw has never even considered being wicked. But when she goes to take her entrance test for a witch academy, she doesn't get the reaction she's expecting -- and is the first kid in memory from the west to be sent to the School for Wicked Witches.