Number One (1976)

Two little girls hide in the boys' bathroom at school so they can find out what happens there. When two boys come in, the four gradually talk each other into taking off their clothes. The principal catches them, and angrily berates them for what they've been up to, warning them that he'll have to tell their parents about the incident. Later repercussions are seen as parents of three of them separately discuss and fight about what has happened, with some taking a winking attitude of their child's discovery and others battling about how to react. Returning to school poses an additional challenge, as everyone has found out what has gone on.