A porcelain-coated steel panel, usually 42 to 48 inches high and of variable lengths, that permits teachers (and students) to write key learning materials with ordinary felt-tipped marker pens for viewing by an entire class. Often as long as the classroom wall itself, dry-erase boards began replacing once-ubiquitous green and black slate CHALKBOARDS in the 1980s and 1990s. Often called market boards, the dry-erase boards are easy to clean with any soft cloth, and they eliminate the problem of chalk dust—often a serious health problem for students allergic to chalk dust and an equally serious problem for classroom computers if the dust invades the inner workings. Dry-erase boards accept markers in a range of colors that increase the instructor’s ability to categorize or emphasize different materials. (See also ELECTRIC CHALKBOARD; WHITEBOARD.)