A mixed-age environment is an important feature of Montessori education. Students work together in classes that span a three-year age group, typically ages 3-6, 6-9 and 9-12 years. All Montessori classes are based on a three-year cycle. Montessori philosophy is based on the growth of the child at their own pace and developmental level.

The children are grouped with others of similar needs in each curricular area, working with older or younger children as appropriate. This arrangement allows each child to learn at his or her own pace regardless of chronological age, and allows students to learn from each other.

The older children have the opportunity to become role models and teachers for the younger children reinforcing what they have learned themselves. The younger children learn from observing and working with the older children. The older child finds themselves in a position of responsibility, and, by showing younger children what he/she knows, affirms to themselves, more surely than any test, the extent of his/her learning. In a Montessori classroom, students are free to choose their own work within limits and remain with that work as long as their interest is engaged. As a result, the atmosphere in a Montessori classroom is calm, non-competitive, and industrious. Such an environment fosters self-confidence and provides a base from which cooperation, understanding, tolerance, and responsibility is learned. Cooperation replaces competition as the driving force within these mini-societies. When three age levels are represented in a class, children connect with others at their developmental level, not just their numerical age.

The social structure of the class is like a microcosm of society, different ages of children working together in harmony. The third year of the cycle allows each child to maximize their individual potential by synthesizing and expanding upon the concepts they have learned. The auto-education facilitated by the prepared environment means that each child is learning and developing at his own pace.