1958: Television.

Back in the day, when a teacher wheeled the AV cart into the room, you knew something important was about to happen. Rocket launch, presidential speech, science programs. TVs gave teachers all sorts of new teaching options, especially when the VCR came along.

In the 1960s, there was a lot of interest in developing TV programming specifically for the classroom.  But gradually the thinking shifted toward creating general educational programming for outside the classroom (Sesame Street and Mr Rogers’ Neighborhood were both created in the late 1960s).  

Televisions continued to be used in the classroom for movies and other programming at the teacher’s discretion, but like radio before it, TV never delivered the major shift in instructional methods that some thought it would.