Concentration

"The first essential for the child's development is concentration. It lays the whole basis for his character and social behavior. He must find out how to concentrate, and for this he needs things to concentrate upon. This shows the importance of his surroundings, for no one acting on the child from outside can cause him to concentrate. Only he can organize his psychic life."
The Absorbent Mind p 202, Chap 22

Montessori did not expect concentration to be a natural characteristic of childhood development. She was well read in the psychological manuals of her day in which it was said that young children were incapable of concentration.

It was her observation of the activities of one child working with the cylinder blocks that led her to question this point and to test it out in other children - That was the seed "After this, whenever I saw a child concentrate on a piece of work I left him undisturbed." (The Child, Society and the World p. 14, Chap II).

This observation led her to see that concentration was, in fact, the key to the natural development of the child. It became the focus of her subsequent work with teachers trained to recognize the importance of its occurrence and the degree to which it released the children to work independently and yet in harmony with each other.

She saw that concentration was not something that could be taught or enforced, but that it was, instead, a vital characteristic of human growth and a demonstration that innate psychic needs were being satisfied.

The moment that a child demonstrated concentration was the moment that led to all the other characteristics that were then associated with 'normalization' (Montessori's word for the child becoming balanced in mind, body and spirit).

"Concentration is the key that opens up to the child the latent treasures within him. As the scattered elements of his personality come together, order begins to take the place of disorder, and the work of self-construction, which had been interrupted, is now taken up again, as nature had intended all along."
Standing, E.M. (1998 edition) Maria Montessori. Her Life and Work p.174, Chap X.