One of the strongest associations many people make with Maria Montessori is her development of hands-on learning materials. These are perhaps the most recognizable and prominent component of the “prepared environment,” and they represent a powerful instrument of the pedagogy. The phrase “Montessori materials” refers to the beautiful hands-on manipulatives on the shelves of our classrooms. And while early educational theorists had developed didactic learning materials, it was Maria Montessori who realized and implemented their use with the greatest insight and success.
If you have heard your child talk about the Pink Tower, the Stamp Game, the Checkerboard, or the Trinomial Cube, these are all examples of Montessori materials. Likewise, puzzle maps, pin maps, grammar boxes, sentence analysis layouts, the Geometry Cabinet, and the Pegboard are Montessori materials. Specifically in Primary classrooms, your child is referring to the Metal Inset work (a material for the development and refinement of the hand), not what is sometimes misheard as the “Metal Insect” work!
Montessori materials have two main characteristics we can identify. First, the material represents an “isolation of difficulty.” Simply put, the material does not attempt too much. For example, the Knobbed Cylinder material teaches discrimination of shape and size by using circumference and depth, but each set shows only one dimension. The second characteristic is the “control of error.” An important aspect of the Montessori pedagogy is its support of independence in the child. By designing materials that are self-correcting, the work becomes more exploratory and more meaningful to the student. The use of bead chains, which are series of bead bars, each with the same number of beads, strung together, with corresponding arrows to label the multiples, illustrates this aspect. If a child mistakenly lays out a “48” label in the wrong position on the 8-chain, the error will eventually reveal itself, as only the multiples of 8 are present in the work.

Maria Montessori used the phrase “sensitive periods” to describe the child’s development within each plane. A sensitive period refers to a time when a child is especially in tune, especially ready, especially compelled to work on activities that satisfy the need of that developmental stage. It is temporary and, if missed, cannot be reacquired. A commonly understood example we can use to illustrate this concept is the acquisition of language. A child in the first plane of development is “wired” to acquire language in much the same way that a plant is “wired” to send out roots or begin to form a bloom. A child who is not provided an environment that supports this sensitive period for speech and communication will have a much more difficult task in attempting to acquire these skills at a later age. In the same way, Montessori identified 11 separate sensitive periods. When we speak of children being “inner directed,” it is to these sensitive periods, a term borrowed from botany, to which we refer. Starting in the first plane of development, they include a sensitivity to movement, music, grace, courtesy, and order. During the second plane of development, from 6 to 12 years of age, the child develops a sensitive period for the use of imagination, for acquisition of culture, and for a strong sense of the social realm. There also exists a strong motivation for the learning of facts and nomenclature, as well as a sensitive period for the study of morality, right and wrong, and justice. A child in the third plane of development, from 12 to 18 years of age, is in a sensitive period for tremendous abstract thought, for delving into great detail on specific topics, for thinking in global terms, and for taking on adult roles.