New technologies come and go but some hang around decades after introduction. For example, the late-19th century chalk blackboard in classrooms morphed into current white (or green) boards.

Consider the overhead projector (OP). While many teachers’ rooms have projectors mounted on ceilings that project Internet images onto whiteboards, just as many teachers have a cart with an overhead projector handy. And even in a desk drawer stacks of transparencies (older readers will nod their heads in agreement but rookie teachers may scratch their heads in puzzlement over just what are transparencies).

So here’s what has happened to a once innovative technology for one generation of teachers to become a ho-hum old technology to a later generation and a head-scratcher to brand-new teachers in 2021.

When were overhead projectors introduced into classrooms?

A 3M employee invented the machine in the early 1960s and within a few years, it had…