This progression was formally codified by Lawrence Kohlberg, a 20 th-century developmental theorist who identified six stages of moral development. According to Kohlberg, early adolescents have usually reached the third stage of moral development: the Conventional Level of interpersonal cooperation.The Conventional Level means they understand morality as determined by social convention and wish to conform to be a good person..his means that teens begin to assess morality by what is best for the most people. As teens get older, they enter the Principled Level of morality, which includes the fifth stage of moral development -- the social-contract orientation. During this stage, teens start looking outside their needs to assess morality.