The use of the materials is based on the young child's unique aptitude for learning which Dr. Montessori identified as the absorbent mind. In her writings she frequently compared the young mind to a sponge. It literally absorbs information from the environment. The process is particularly evident in the way in which a two year-old learns his native language, without formal instruction and without the conscious, tedious effort which an adult must make to master a foreign tongue. Acquiring information in this way is a natural and delightful activity for the young child who employs all his senses to investigate his interesting surroundings.
Since the child retains this ability to learn by absorbing until he is almost seven years old, Dr. Montessori reasoned that his experience could be enriched by a classroom where he could handle materials which would demonstrate basic educational information to him. Over eighty years of experience have proved her theory that a young child can learn to read, write and calculate in the same natural way that he learns to walk and talk. In a Montessori classroom the equipment invites him to do this at his own periods of interest and readiness.
Dr. Montessori always emphasized that the hand is the chief teacher of the child. In order to learn there must be concentration, and the best way a child can concentrate is by fixing his attention on some task he is performing with his hands. (The adult habit of doodling is a remnant of this practice.) All the equipment in a Montessori classroom allows the child to reinforce his casual impressions by inviting him to use his hands for learning.
[A Parent's Guide to the Montessori Classroom by Aline D. Wolf]