Moral Development Theory was established by an American Psychologist named Lawrence Kohlberg. Kohlberg served as a professor at both the University of Chicago and Harvard University, where he specialized in research releated to moral education and reasoning. His theory was influenced by Jean Piaget's Theory of Cognitive Development which suggests that the development of intelligence occurs in four stages, beginning with the most basic and ending at the most complex.
Moral Development Theory suggests that children pass through six stages of development when acquiring moral reasoning skills. Each child must pass through the different stages in order; however, not all children will reach all six stages. In fact, Kohlberg suggests that individuals who reach stage six are incredibly rare. Additionally, Kohlberg suggests that Moral Development Theory is applicable to individuals of all cultures at any given point in time.