Wiki got this one absolutely correct. When they first got started at my small, country high school, the sixth period of one Friday each month was devoted to a sock hop. Later on, teen clubs were "invented," and the sock hop was either a Friday or Saturday night entertainment - if we could beg our parents into dropping us off. I should add that there were always 4-5 parent or teacher chaperones at the night events.
During the late-1960s, I actually moonlighted from being a teacher to running a teen club every Friday night. I met my first fiance there - he was a Rent-a-Cop. My students were very upset that I was dating a policeman. When I ended up marrying a vice principal, they were even more upset!
Oddly enough, the teen clubs were financially supported by The Maryland-National Capital Park and Planning Commission, the same government agency that I work for today as director of Surratt House. I guess it was fate.