Catholic Girl Sinners Killed by Headmistress

by Moses
(South Carolina)

A long time ago, when I was much younger, I saw a movie late at night. It had something to do with a Catholic all girls school.

The girls were trouble makers, and would sneak out to meet some guy in the ground keepers shack to fulfill certain "sins".

The thing that set it off was the crazy headmistress who was killing the girls (I believe) by using secret passages.

The title of this film is still bugging me to this day. Can anyone help?