L'âge bête (1980)

Julien and Hervé are at odds with their math teacher, a woman whose lack of experience makes her job hard to do, facing defiant students. She has them expelled from school. To take vengeance on her, they decide to kidnap her and to hold her prisoner in a shed in the woods during three days; but she's a diabetic and needs insulin, besides, one of the teenagers has an accident.