In its fledgling state of development, this branch of psychology focused almost exclusively upon issues related to the developmental learning in infancy and early childhood. Subsequent development under the leadership of key figures in the field of education such as Marie Montessori, Jean Piaget, and Erik Erikson saw developmental psychology as it came to be called evolve into one of the most active and vital sub-specializations within psychology. Under the leadership of Karen Horney, Melanie Klein, and Anna Freud, psychopathology moved into the field of child development and created a whole new area of specialization in clinical psychotherapy as I have explored in my 2019 book, Child Psychopathology in Clinical Practice. In the following study, we will concentrate our attention upon child development and stay within the confines of developmental psychology as it has come to be known and defined. Though our interest here will be upon the learning spectrum of child development demonstrated in the pioneering work of Montessori, Piaget, and Erikson, we will begin with a general overview and introduction of the broad field of developmental psychology itself before focusing our attention upon the learning spectrum as explored by our three pioneers.