Maria Montessori's approach reflects a theoretical kinship with the European progressive educational philosophers Rousseau, Pestalozzi, Seguin, and Itard. She believed in children's natural intelligence, involving from the start rational, empirical, and spiritual aspects. She saw development as a series of six-year periods, like repeating triangular waves, each with its own particular sensitivities. A constructivist, she posited an active child, eager for knowledge and prepared to learn, seeking perfection through reality, play, and work. In Montessori education, children usually are grouped into multiage classrooms spanning three years, in order to promote adult-child continuity and close peer relationships. Birth to age 3 is the time of the "unconscious absorbent mind," whereas age 3 to 6 is the time of the "conscious absorbent mind" (Montessori & Chattin-McNichols, 1995). In both, the child seeks sensory input, regulation of movement, order, and freedom to choose activities and explore them deeply without interruption in a carefully prepared (serene and beautiful) environment that helps the child choose well (Greenwald, 1999).