Killing Mr. Griffin by Lois Duncan

Kill their English teacher? Even if Mr. Griffin was the toughest teacher in the school, the one who demanded the most, gave the lowest grades, and refused to turn the classroom into a place where students had 'fun'—there was no reason to kill him. Or was there?

Well, Mark suggested, perhaps not kill him—just really frighten him. Kidnap him for a few hours and teach him that students could strike back.

No, they never actually intended to kill Mr. Griffin. But sometimes even the best-laid plans go wrong.