Stages of Development Series: Maturity

LakeCreek Montessori School • March 5, 2025

Explore the final stage of human development (ages 18-24) through a Montessori lens—where independence, purpose, and meaningful societal contributions take shape.



This is the final post of a series focusing on each of the four stages (or planes) of development: birth through age six, ages six to twelve, ages twelve to eighteen, and ages eighteen to twenty-four. Montessori pedagogy calls for a big picture perspective that incorporates the fundamental principles of human development at each stage of development and how we can best provide for a developing young person in each stage.


A Path Toward Maturity and Contribution to Society


The journey of human development, as envisioned by Dr. Maria Montessori, is marked by four distinct planes. Each plane represents a different phase in an individual's growth, and the fourth plane, spanning from 18 to 24 years of age, is no exception. This phase, which Montessori refers to as Maturity, signals the culmination of psychological and physical growth and paves the way for young adults to step into the world as a fully formed individuals capable of significant contributions to society.


Characteristics of the Fourth Plane


The fourth plane represents a time when individuals reach the height of their development and begin to assume their role in society. Unlike the earlier planes, the psychological changes during this period are less dramatic and more internal, and the focus shifts to understanding oneself and the world beyond one’s immediate needs. Whereas the body completes its physical maturation, the mind embarks on the task of understanding how it can contribute to humanity.


In The Four Planes of Education, Dr. Montessori writes, “The individual should be the man who knows how to make his own choice of action having passed to perfection the preceding phases. He should be as a live spark and aware of the open gate to the potentialities of prospective human life and of his own possibilities and responsibilities” (p. 15). This encapsulates the essence of the fourth plane— young adults’ newfound ability to make independent choices while being aware of their potential impact on society.


In this stage, individuals are not merely focused on themselves but are also learning to engage with the world beyond their personal ego. The question that arises is not “Who am I?” but “What can I do?” This shift from self-centeredness to a broader, more collective view of life signifies the maturity that defines the fourth plane.


Conquest of Independence

One of the key aspects of the fourth plane is the conquest of independence, particularly economic independence. This phase marks a time when individuals strive to become self-sufficient within the larger society. Young adults move beyond the dependency of childhood and adolescence, assuming more responsibility for their own life, finances, and future.


This is a period when a personal mission begins to take shape. Young adults start to solidify their goals, whether academic, professional, or personal, and work toward them with a growing sense of purpose. Dr. Montessori believed that achieving economic independence was crucial, as it not only provides the means to live but also fosters a sense of autonomy and responsibility.


Observable Examples of Development


Physically, by the fourth plane, development is largely complete. The dramatic growth spurts of the previous stages have slowed, and young adults now have full mastery over their body. Health is typically stable, and there is an overall sense of well-being.


Much like the second plane, the fourth plane is also conducive to intellectual pursuits, particularly those that lead to specialization in areas essential for a future career. This is when our young adults are honing skills that will serve them in the professional world, whether through higher education, apprenticeships, or other forms of specialized learning.


The fourth plane is also a time when individuals, having developed a solid understanding of themselves, are ready to take on more significant intellectual and social responsibilities. This is when they truly start asking the big questions, such as, “How can I contribute to the world?” It is at this stage that young adults embark on the exploration of their "cosmic task," a concept Montessori introduced in the second plane, which refers to the idea that every individual has a unique role to play in the larger story of humanity.


The Role of the Supportive Environment


With significant internal growth happening during the fourth plane, the role of the external environment remains crucial. A supportive environment during the preceding planes can have a profound effect on how individuals move through this stage. If our young adults have been nurtured in an environment that promotes autonomy, responsibility, and respect for their capacity to make choices, they are more likely to enter adulthood with the skills and mindset necessary to thrive in society.

To prepare for their careers during this time, many young adults pursue higher education, either through university studies or vocational training. Alternatively, they may enter the workforce, beginning to take on professional roles that contribute to society. This is also a time when many young adults leave the family home and start families of their own, further solidifying their place in the world as independent adults.


Dr. Montessori, unfortunately, did not have the opportunity to explore this phase in depth. However, we can imagine a world where every individual has been given the best possible environment throughout the previous planes of development. In such a world, adults who emerge from the fourth plane are equipped not only with the knowledge and skills to succeed but also with a profound sense of responsibility toward the greater good.


An Enlightened Society


The ideal outcome of the fourth plane is individuals who not only seek personal success but also work toward the welfare of humankind. Young adults who have passed through the earlier planes of development with the support of nurturing environments can enter society with a strong social conscience, eager to contribute to the collective well-being of humanity. They see the interconnectedness of all people and seek ways to address societal issues and contribute to the common good.


Imagine a world in which all young adults, having been guided through the previous developmental stages, emerge from the fourth plane ready to play their roles in society—not only as self-sufficient individuals but as enlightened members of a larger human community. This vision encapsulates the Montessori ideal: a world where everyone has the potential to contribute meaningfully to the advancement of humanity as a whole.


The fourth plane of development is not merely a time for self-discovery but a time for self-realization and societal contribution. Young adults, secure in their independence, prepare to engage with the world in ways that transcend personal goals, focusing instead on broader responsibilities. By fostering an environment that nurtures growth and independence, we set the stage for a society composed of individuals capable of making meaningful contributions to humanity’s collective well-being.


Curious to see how attention to the characteristics and needs of earlier stages of development can support an enlightened society? Schedule a tour today! 



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Have you ever watched a child trace the outline of a window with their finger, or carefully line up blocks into a perfectly symmetrical row? They may not have a name for what they're doing, but they are already exploring geometry. Dr. Maria Montessori understood that geometry is not an abstract school subject. It is part of the world children live in from the very beginning. A glance at the typical geometry textbook might suggest otherwise. Formulas, diagrams, and definitions can feel remote and lifeless, something to be memorized and forgotten. But look around for a moment. There is geometry in the angles of a mineral crystal and in the symmetry of a butterfly's wings. There is geometry in the legs of a chair and in the steel girders of a bridge. Children encounter it everywhere! In fact, research suggests that a basic intuitive understanding of geometric concepts may be inborn in human beings. A fascinating study of the Munduruku (an indigenous group living in the Amazon whose language includes very few spatial or geometric terms) found that both adults and children demonstrated an intuitive grasp of basic geometric ideas. This isn't something they were taught. It was already there. Montessori classrooms build on exactly this kind of inborn understanding. From Sensory Experience to Big Ideas In the early childhood years, children work with geometry through their hands. Materials like the Constructive Triangles, the Metal Insets, and the geometric cabinet give children a felt, physical understanding of shape, symmetry, and form before we introduce any formal terminology. Children gather and store these impressions. Their minds are being prepared. As they get older and certainly in the elementary years, children are ready to bring names and reasons to what they already sense. Elementary-aged children don't just want to know what something is called. They also want to know why. Why is this shape called a pentagon? (Spoiler: Its name comes from the Greek word for five: pente.) Geometry becomes a doorway into the history of language, ancient Greece, and the lives of mathematicians like Thales, Pythagoras, and Euclid, who puzzled over the same ideas thousands of years ago. This is the spirit of Cosmic Education when we pull one thread of curiosity to find it unravels into history, language, culture, and mathematics! Geometry, Algebra, and Arithmetic Woven Together One of the things that makes Montessori's approach to geometry so distinctive is that it doesn't stand alone. In the Montessori classroom, geometry is part of a three-part approach to mathematics, interwoven with arithmetic and algebra in ways that make each of them easier to understand. The Binomial Square is a good example. It presents the algebraic expression of (a + b)² = a² + 2ab + b² as a geometric pattern of squares and rectangles that children can actually build and hold. The arithmetic follows the pattern. The pattern confirms the algebra. Each one reinforces the others, and the whole thing is far more memorable than just a formula written on a board. Open-Ended, Creative, and Genuinely Fun Plus, a lot of Montessori geometry work has no single correct answer. We invite children working with the Metal Insets or Constructive Triangles to find as many equivalent figures as they can for a given shape. There may be dozens of ways to approach the same problem. This open-endedness nurtures the creative, analytical thinking that elementary children are hungry for. Plus, this quality of thinking will serve them in every area of life. Compass-and-straightedge constructions are another example. These beautiful, precise drawings challenge children in a way that is both mathematical and artistic. Many children find them deeply satisfying. What This Looks Like at Home You don't have to wait for the classroom to feed your child's geometric curiosity. Point out the shapes in a honeycomb. Notice the angles in a spider's web. Talk about the tiles on the floor or the panes in a window. Ask your child questions. Do you think that could be a triangle? How many sides does it have? These small moments of noticing are the same thing Montessori described when she wrote about preparing the environment to reflect the world children already live in. Geometry is already there. We're simply helping children see it. Come visit us in LakeCreek Montessori School to see how this unfolds in the classroom and to watch children fall in love with one of humanity's oldest ways of understanding the world.

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