The child in a Montessori classroom learns to control a pencil by filling in outlines, an activity which does not weary him or her because he or she enjoys it. To make the outline, he or she uses equipment known as the Metal Insets. Each inset represents a different geometric shape. After selecting a figure and tracing it on paper, the child fills in the outline with a colored pencil of his or her own choosing.
After the child has worked for a while with the Metal Insets and the Sandpaper Letters, a day comes when he or she realizes that he or she is able to make words with a pencil. Montessori called this phenomenon the explosion into writing. (Montessori, 1967, p. 84).