Erwin C. Dietrich - Julchen und Jettchen, die verliebtenApothekerstöchter AKA Come Play with Me 3 (1980)

Synopsis IMDB:
Comedy about some schoolgirls being taught anatomy (of the sexual nature) by the sexually frustrated Barbara Moose. In bed at nighttime the girls practice their daily lessons on each other and on any unsuspecting visitors of the night. When they're not in class they enjoy frolicking around outside (naked most of the time!) experiencing the joys of nature.