One of the greatest thoughts concerning how people developed their moral reasoning was from Lawrence Kohlberg who developed the Six stages of Moral Development.  He emphasized peer interaction in order for a person to take the role of another person.  It has met with criticism, such as too much emphasis on moral thought, but not as much on moral behavior.  Kohlberg's theory has also been criticized that it did not recognize gender differences, and is culturally biased.  Despite these criticisms, Kohlberg led people to a better understanding of how people develop the notion of right and wrong.