6 suecas en el internado

Although Six Swedes on a Campus and Amorous Sisters seem to have most of the same cast & director, not to mention basic premise, they are different in content. Amorous Sisters is much shorter (about 65 mines), but contains slightly stronger material, and Six Swedes on a campus seems to be better made, and more of a full-length movie. In 6 Swedes, the girls mess around with the rather camp muscle-bound PE teacher outdoors, whereas in Amorous Sisters, he's pounced upon inside.

Perhaps there was originally one big movie, and was then made into little ones. I'd say 6 swedes was the better one, because the film quality is higher. Don't bother with 6 Swedes in Ibiza by the way, it's rubbish: 6 Swedes at the pump is OKish, but beware of the 6 Swedes at the Alps - the version I had which is supposedly uncut is very tame.