Our modern day chalkboards, with their greenish cast and dustless chalk, have gone through many stages of evolution. At first, chalkboards were merely small squares of slate, framed with wood to keep them from breaking, and marked on with other shards of slate. In the early 19th century America, these rudimentary instruments were widely used in public schools, because paper was too expensive.

A leap forward occurred when a geography teacher in Scotland was reputed to have gotten the slates off student's laps and up onto the wall. The earliest record in America shows instructors utilizing them in academic military schools, such as Westpoint, in 1801. Teachers no longer had to spend so much time writing individual problems and lessons on a single student's slate, but could speak to an entire class where everyone had the benefit of seeing the board.

This revolution in educational method ran parallel to other innovations in America in railroads and mining. Slate, a dark, metamorphic rock, was mined out of Vermont, Maine, Pennsylvania, Virginia, Maryland, and New York. It could then be transported via railroad to the thousands of prairie schools popping up across the frontier in the 1840s.

By the 1850s, most one-room schoolhouses were outfitted with the staples: a wood burning stove, benches, and a large blackboard. In poorer or more remote schools, teachers might resort to painting a plaster wall or wooden panel with dark paint to imitate the slate. An old rag served as eraser. Each school could now accommodate more students and teach them more efficiently.

The basic tool has been somewhat modernized. We're more likely to find a chalkboard that is a steel sheet enameled with porcelain in today's classroom. Also, bits of slate were replaced by chalk, which is a white limestone mined from the earth. Of course, rag erasers were replaced by blocks of felt that could erase chalk marks without creating as much airborne dust. However, despite all these changes, the blackboard remains the centerpiece of the classroom.

In the 1990s, concern over allergies and other potential health risks posed by chalk dust prompted the replacement of many blackboards with whiteboards. A whiteboard is a plastic board, otherwise known as a dry erase board, which uses special pens to make colored marks. They can be a cleaner, brighter alternative to education and business interests.