The middle school that I went to had a ~14" crt tv hanging from a sturdy ceiling mount in every classroom.
Displayed things like school bulletins and daily morning announcements, there was a couple educational channels, and a vcr input. Every now and again there'd be some sort of presentation instead of hauling everyone into the gym for a school assembly.
Anyway; it didn't take me very long to figure out the universal remote that came with the satellite receiver at home could be programmed to the school TVs. I'd mess with the one in class, or skip classes and mess with the ones in my friends classrooms through the windows; cranking up the volume and blasting Bill Nye or the announcement channels awful elevator music. Weekends, I'd do a lap of the school turning on all the TVs I could reach from outside and maxing the volume for whoever opens on Monday, or just turning them off again so it blares at whoever turns it on next.