Does anyone know the name of this violent prep school film?

This movie came out around the late 80's-early 90's. It was about a
group of teenage boys at a prep school or academy of some sort that
may have been military or religiously based because they seemed
isolated from the outside world and there was a teacher who was
extremely violent and mean to the boys. There was a particularly
brutal scene where the teacher pushes one of the boys down on his desk
and whips him repeatedly with a sharp metal pointer. The pointer
appears regularly in the film and is the teacher's weapon of choice
when threatening the boys. I think the teacher was male, perhaps of a
high military ranking or some kind of war background. He may have been
scarred on his face. I don't think the film has a particularly happy
ending, although the boys do find a way to get back at their teacher.

Note: This is NOT a pornographic or SM film. It was a drama that I
vaguely remember was inspired by true events.