I'm not sure how related they are, but I'm almost certain that Lost and Delirious is a remake of this movie (or the story that it's based on). Very similar plotline, and even some of the scenes and sets seem to be very, very similar. Lost & Delirious is actually a much better movie, so see that one instead.
This one moves very slowly, but being a late 60s French movie, that is to be expected of the style. Told in a retrospect from the perspective of one of the girls revisiting the school. The editing of the flashbacks with the current scenes is a little bit confusing at first, particularly since the audio from each overlaps (ie, hearing flashbacks while seeing the present and vice versa). Also, the "girls" are a bit old to think that they are in a boarding school. Finally, not much character development to even get you attached to the movie.