Blackboards
 The first blackboard used in a school was in Philadelphia in 1809. Early blackboards were made from pine lumber and covered with a mixture of egg white and carbon from charred potatoes. Teachers and students wrote with chunks of chalk and erased with cloth rags. When slate boards became available, teachers used cylinders or white, soft chalk and a felt eraser. These blackboards and slate boards were laborious apparatuses, and the accompanying chalk dust was the bane of all teachers.
The blackboard was an important instructional device, allowing the teacher to illustrate lessons by directing the attention of the entire class. Consequently, its use required the teacher to be constantly at the front of the room, and pedagogy was entirely teacher-centered. 
Today the blackboard is still common, but is slowly being replaced by the whiteboard, a plastic composite of the same size and shape. The teacher writes on the board using color, erasable pens. No longer are classrooms covered in chalk dust, and whiteboards eliminate the piercing shrill chalk can sometimes make when coming in contact with the blackboard!
Teachers today are less dependent on blackboards and whiteboards. When presenting information to the whole class, teachers may opt to use an overhead projector or computer with presentation software. However, many teachers prefer to circulate among students in the room and work with them one-on-one or in small groups.
Then & Now:
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