Dr. Montessori believed that growth, development, and learning happen in waves. She determined that children go through four distinct periods of development, which she called the planes of development. The four planes occur from birth–6 years old, 6–12 years old, 12–18 years old, and 18–24 years old. In each plane, children and youth are drawn to different skills and activities, and Dr Montessori believed that they can make enormous progress if they have opportunities to explore and practice these skills.

The first plane is a time of monumental growth and development as the baby grows and learns to move, balance, develop coordination, learn to speak, and exercise her own will. All exploration is done through sensory experiences found within their environment. During the first plane, the child moves from unconscious to consciousness. It is, Montessori observed, “the most important period of life is…the first one, the period from birth to the age of six. For that is the time when man’s intelligence itself, his greatest implement, is being formed.” (Montessori, The Absorbent Mind, p. 21)

A Closer Look at Montessori's Second Plane of Development

The second plane is time of “the development of the self as an individual being.” (Lillard, Montessori Today, p. 24) During this timeframe, the child has a need to acquire knowledge about himself and the universe. It is also a time of steady physical growth. We can see that the child is physically leaving babyhood behind. He loses his baby teeth, and his body loses its rounded baby features as his legs and torso lengthen, becoming similar to an adult. The child’s immune system becomes stronger. In general, this plane of development is marked by “great strength and robustness of body and mind; a fact indicated by a distinct falling off in the incidence of sickness and mortality. It is a period of comparative calmness and serenity.

During these years children are capable of accomplishing a great deal of mental work.

It is their ‘years of plenty’; and if given the right opportunity and right means, they will lay up a great store of cultural information.” (Standing, Maria Montessori: Her Life and Work, p.113)

Conventional education and child development theory sees development as a linear progression, where growth progresses at a steady rate every year, for 18 years. Dr. Montessori, on the other hand, observed that children develop in four separate planes. And within each plane, there is a birth, a peak, and then a decline (or valley) as the child prepares for the next plane.

Montessori education is geared to peaks and valleys of human formation

Traditionally, we educate children based on the conventional idea of linear progression. This means that each year, we steadily increase the amount and the difficulty of information that we present to the children. And each year, more and more study is involved. This practice assumes that all children grow and learn at the same rate of development. The flaw with this system is that it assumes that intelligence increases with age. (Lillard, 1996) Children who fall behind face remediation and are also held accountable for next year’s learning.

The three-year groupings of Montessori classrooms allow lower and upper elementary students to develop at their own speed.

Children do not have to complete the same tasks at the same time. They have the freedom to explore concepts more thoroughly and as they are ready for them. Students are encouraged to research a single idea in various ways, building both the breadth and the depth of their understanding.