Whatever is done in school, there are bound to be mistakes. What matters is not so much correction in itself, as that each individual should become aware of his own errors. Each should have a means of checking, so that he can tell if he is right or not.

Maria Montessori, The Absorbent Mind

The control of error through the material makes a child use his reason, critical faculty, and his ever increasing capacity for drawing distinctions. In this way a child's mind is conditioned to correct his errors even when these are not material or apparent to the senses.

Maria Montessori, The Discovery of the Child