Little Girls Blue (1978)

Two young girls at the Townsend School for Girls, a private high school, plot to escape for the evening with their dates, shunning their younger friend Buffy because she's still too young and "still a virgin." Indignant, the young-looking (15 or so) Buffy decides to prove herself by seducing her history teacher in exchange for an A+. Meanwhile, Coach Fowler fantasizes about his student Miriam, the two of them making love in all-white environs. The two older girls escape with their dates and have a fine time in the woods, though one gets a surprise at an old cabin when her date has brought along a friend. The next day, they plot to seduce Coach Fowler in the guise of Miriam in a darkened room, and the girl who took advantage of him leaves the poor man dazed and confused...