On the infrequent occasions we had any sort of "media" in school it was usually in the form of 16mm film on a cart that was used to move the projector and an approximately 25 inch diagonal rear projection screen.
That's the first I've heard of schools using rear-projection screens. In my school days, most classrooms had a roll-up screen at the front of the room. If there wasn't one, we had portable screens on tripods. And in high school, I was one of those projectionist geeks on the Audio-Visual crew. It was an easy class credit, and you got to see all the films that came in every week.
Some of the more memorable -- and unintentionally funny -- school films were the anti-drug ones with titles like LSD: Insight or Insanity?
Which makes me curious about how health classes (maybe they don't even call it "health" anymore) have changed. What are kids learning these days about sex and drugs? (I mean inside the classroom.)