1925: Film Projector.

When Thomas Edison invented the projector he believed it would put school books out of business; visual learning would rule. Though film projectors did eventually become a classroom staple, there were a lot of obstacles to their success. The up-front cost of a single projector was around $150 in the mid-1930s, making it an expensive purchase for school districts.

There were also compatibility issues. Not all film reels were the same size. Some schools also initially purchased silent film projectors, which quickly become obsolete.