I took a developmental child psychology class right after I received my Montessori certification. It covered mostly Piaget, Skinner and Rogers, of course, not one word about Maria Montessori. What was one of the most accurate things I learned was that Montessori’s 4 Planes of Development was a new way of looking at human development in the early 1970s. Infancy was a time of profound change and development, the preschool years were hands-on, concrete, grade school was more abstract, developing concepts of right and wrong, and the teen years were turmoil (I remember vividly an illustration of teens wearing leather jackets with labels, such as paranoid, schizophrenic, manic, etc!-not to worry though because “these symptoms usually disappeared after puberty”. The final stage was youth, it lasted through the 20s. The theory was that life was more complicated and the youth stage was needed to become an independent and stable person.