Mom offers group sex as therapy for all problems

The guy and his girlfriend go home after school, but on the way they are caught up by a pretty teacher who invites a couple for a ride, and then drop in for a visit. Being a real teacher, the lady leaves the couple alone, quietly spying on the sex of the young and getting excited in earnest. As a result, the mentor falls on the tail of the lovers and does the right thing, because who else will teach future spouses what a dumb sin is and how to get pleasure from it.