Montessori called this the "constructive rhythm of life." The sensitivities of each stage guide the development and determine the rhythm of movement through the planes. (Camillo Grazzini, "The Four Planes of Development", p. 31, Namta Journal, Vol. 29, No. 1, Winter 2004).
In addition, each plane contains two sub-phases, each lasting about three years. These sub-phases also parallel the movement of creation and development. In general, the first three years of each plane are for creation, and the last three years for development, or "crystallization." The sub-phases emphasize the movement of progression and recession within each plane, and are of particular importance in preparing an environment best suited for the needs of the young person. The planes of development can also be thought of in terms of a type of metamorphosis. If we think of the appearance, needs, and life of a caterpillar, we see a completely different creature than the butterfly it will later become. The caterpillar crawls along eating leaves, the butterfly flies from flower to flower in search of nectar. We cannot aid the caterpillar by providing a garden full of flowers, nor will the butterfly benefit from green leaves. The child, too, is quite different at each stage of development, and needs very different conditions in order to thrive. There are identifiable mental and physical characteristics at each plane, and the child's environment must change to respond to those characteristics. Each plane has specific developmental objectives. The child develops certain sensitivities or abilities at each plane in order to meet these objectives.
If the child has not satisfied all of his needs at one stage, he moves into the next with a deficit. This deficit cannot be made up naturally, but only with conscious effort using the characteristics of that plane. Some creations, such as learning a language, will never be the same as if they were learned in the optimal developmental plane for that particular ability.
