Night School — Caroline B. Cooney

A mysterious teacher casts a spell over his class and assigns dark, evil homework in a class that Mariah wishes she had never signed up for--a class where she is trapped and can never escape.

Mariah's not sure why she's signed up for the mysterious night class. The notice on the board gives no clue as to the subject, but something compels her to add her name to the list...

Only three other people have signed up. So it's a very select class, but then the subject requires special skill and attention...

For they are all learning the art of fear. And their teacher demands results. But there's no easy way to make the grade...in terror...