I remember seeing a movie on TV, more than once, it had to be in the 70's and I remember it was in color, the setting was probably the early 30's or 40's, a boarding school for girls and they go on a picnic and one or more of the little girls disappear. I don't remember if it involved murder. Could even have been set earlier because I remember that the women had on long dresses, the little girls all wore dresses, but I am sure there were cars, very old. I know it was in color. Racking my brain. Hate it when I remember part of something but not all. Anyone have any ideas?

Picnic at Hanging Rock (http://www.imdb.com/title/tt0073540/)