Witch Week (The Chrestomanci Series, Book 3) by Diana Wynne Jones
Glorious new rejacket of a Diana Wynne Jones favourite, featuring Chrestomanci - now a book with extra bits!
SOMEONE IN THIS CLASS IS A WITCH
When the note, written in ordinary ballpoint, turns up in the homework books Mr Crossley is marking, he is very upset. For this is Larwood House, a school for witch-orphans, where witchcraft is utterly forbidden. And yet magic keeps breaking out all over the place - like measles!
The last thing they need is a visit from the Divisional Inquisitor. If only Chrestomanci could come and sort out all the trouble.