Since shape is the defining characteristic of each letter of the alphabet, Dr. Montessori designed several sensorial exercises to make the children aware of this quality. She began with the geometric solids. This is a set of materials alike in color and texture and of approximately the same size but differing from each other in shape. The set includes the cube, the cone, the cylinder, the pyramid, the rectangular prism, and the triangular prism.
The children learn to recognize these shapes by handling the solids, looking at them, and playing group games where they try to identify the shapes while wearing a blindfold. They also learn to relate the solids to common things in the environment; for example, the sphere is like a ball; the cylinder is like a drinking glass; the cone is like an ice cream cone.
Vocabulary building is an important part of this activity. Children enjoy the challenge of big terms like cylinder, pyramid and rectangular prism. It is much easier for children to learn what a pyramid or a sphere is when they can hold it in their hands, than it is for them to learn it later in abstract form. When they study geometry in future years, children who have been in a Montessori class will have the necessary vocabulary based on concrete representation.