Montessori education is fundamentally a model of and an educational approach based on two basic elements. First, children and adults engage in psychological self-construction by means of interaction with their environments. Second, children, especially under the age of six, have an innate path of psychological development. Based on her/ his observations, Montessori believed that children at liberty to choose and act freely within an environment prepared according to her / his model would act spontaneously for optimal development.
Montessori saw universal, innate characteristics in human psychology which her/ his son and collaborator Mario Montessori identified as "human tendencies" in 1957. There is some debate about the exact list, but the following are clearly identified
- Orientation to the environment
- The “Mathematical mind”
In the Montessori approach, these human tendencies are seen as driving behavior in every stage of development, and education should respond to and facilitate their expression.
Montessori's education method called for free activity within a "prepared environment", meaning an educational environment tailored to basic human characteristics, to the specific characteristics of children at different ages, and to the individual personalities of each child. The function of the environment is to allow the child to develop independence in all areas according to his or her inner psychological directives. In addition to offering access to the Montessori materials appropriate to the age of the children, the environment should exhibit the following characteristics
- Construction in proportion to the child and his/her needs
- Beauty and harmony, cleanliness of environment
- An arrangement that facilitates movement and activity
- Limitation of materials, so that only material that supports the child's development is included
Absorbent mind: Montessori described the young child's behavior of effortlessly assimilating the sensorial stimuli of his or her environment, including information from the senses, language, culture, and the development of concepts with the term "absorbent mind". She believed that this is a power unique to the first plane, and that it fades as the child approached age six.
Sensitive periods: Montessori also observed periods of special sensitivity to particular stimuli during this time which she called the "sensitive periods". In Montessori education, the classroom environment responds to these periods by making appropriate materials and activities available while the periods are active in the young child. She identified the following periods and their durations
- Acquisition of language—from birth to around six years old
- Order—from around one to three years old
- Sensory refinement—from birth to around four years old
- Interest in small objects—from around 18 months to three years old
- Social behavior—from around two and a half to four years old
Normalization: Finally, Montessori observed in children from three to six years old a psychological state she termed "normalization". Normalization arises from concentration and focus on activity which serves the child's developmental needs, and is characterized by the ability to concentrate as well as "spontaneous discipline, continuous and happy work, social sentiments of help and sympathy for others."
The second plane of development extends from around six to twelve years old. During this period, Montessori observed physical and psychological changes in children, and developed a classroom environment, lessons, and materials, to respond to these new characteristics. Physically, she observed the loss of baby teeth and the lengthening of the legs and torso at the beginning of the plane, and a period of uniform growth following. Psychologically, she observed the "herd instinct", or the tendency to work and socialize in groups, as well as the powers of reason and imagination. Developmentally, she believed the work of the second plane child is the formation of intellectual independence, of moral sense, and of social organization.
The third plane of development extends from around twelve to around eighteen years of age, encompassing the period. Montessori characterized the third plane by the physical changes and adolescence, but also psychological changes. She emphasized the psychological instability and difficulties in concentration of this age, as well as the creative tendencies and the development of "a sense of justice and a sense of personal dignity." She used the term "valorization" to describe the adolescents' drive for an externally derived evaluation of their worth. Developmentally, Montessori believed that the work of the third plane child is the construction of the adult self in society.
The fourth plane of development extends from around eighteen years to around twenty-four years old. Montessori wrote comparatively little about this period and did not develop an educational program for the age. She envisioned young adults prepared by their experiences in Montessori education at the lower levels ready to fully embrace the study of culture and the sciences in order to influence and lead civilization. She believed that economic independence in the form of work for money was critical for this age, and felt that an arbitrary limit to the number of years in university level study was unnecessary, as the study of culture could go on throughout a person's life.