Through forty years of constant observation and experimentation, Maria Montessori developed her approach to education. The Montessori approach is concerned foremost with the development of human potential. This approach is based on "following the child", on recognizing the developmental needs and characteristics of children of each age group and constructing the corresponding environment that best meets these needs. Maria Montessori observed that the child moves to adulthood through a series of developmental periods, which she called the Planes of Development. Each period is different but is built on the foundation of the preceding one with the Montessori environment and approach tailored to meet the child's needs at each stage. 

There are four planes of development. In the first plane from birth to age six, the child is characterized by their "absorbent mind", absorbing all aspects of their environment, language and culture. In the second plane from age six to twelve, the child uses a "reasoning mind" to explore the world with abstract thought and imagination. In the third plane from twelve to eighteen, the adolescent has a "humanistic mind" eager to understand humanity and the contribution he or she can make to society. In the last plane of development from age eighteen to twenty-four, the adult explores the world with a "specialist mind" taking his or her place in the world. Maria Montessori believed that if education followed the natural development of the child, then society would gradually move to a higher level of cooperation, peace and harmony.