Each of the three levels corresponding to different ages consists of two stages. The first stage of the preconventional level of moral development is obedience. At early ages, children understand that rules are made by adults and must obey the rules to avoid punishment. In the second stage, children develop the concept of exchange and negotiation, so children do what as asked if the children get something in return. Revenge is considered a way to re-establish justice, so when a child is hit, he hits back.
Stage three refers to a child's desire to act like her peers to be accepted and appreciated as social entities. The fact that a certain group behave in a specific way justifies her own similar behavior, as she seeks the group's approval; morality is, at this stage, what other people think is right and moral. Those who don't fall within the group standards are excluded or punished by collective agreement. The fourth stage involves society and duty as factors of moral development. At this stage, teenagers and young adults begin to acknowledge authority and to understand the consequences of not respecting it.
Stage five refers to morality as a result of individual reasoning. The moral agent is decided by logically applying abstract, universal rules to a concrete situation. Punishment by law is the accepted moral standard and forcing an individual to pay his debt to society is rejected as being unjust and in disagreement with individual rights and welfare. Stage six is attained by few people who behave according to universal moral principles that dictate equality and justice for everybody and recognize that a person's rights are as important as the rights of others.
Kohlberg's theory on moral development has met some opposition in terms of the validity and reliability of his research findings and choice of subjects. By choosing only male subjects for his research, Kohlberg was accused of being biased; according to his studies, women are placed in stage three of moral development, thus inferior to men. Carol Gilligan, Kohlberg's colleague at Harvard and a teacher of Psychology, argues that his system is man-centered and that women and men understand relationship differently, thus there is no one absolute conclusion that can be drawn from Kohlberg's study.