Selman has argued this same point, also noting that the growth of role taking ability is brought on by the child's decreased egocentrism as he/she ages. Lawrence Kohlberg argued that higher moral development requires role taking ability. For instance, Kohlberg's conventional level of morality (between ages 9 and 13, roughly), involves moral stereotyping, empathy-based morality, alertness to and behaviour guided by predicted evaluations by others, and identifying with authority, all of which require role taking. Selman tested 60 children, ages 8 to 10, on Kohlberg's moral-judgment measure and two role taking tasks. He found that the development of role taking, within this age range, related to the progression into Kohlberg's conventional moral stage. A retest a year later confirmed Kohlberg's argument, and in general, it was shown that higher moral development at the conventional stage requires children's achieved ability at this age to reciprocally deal with their own and others’ perspectives. Mason and Gibbs found that moral judgment development, as measured by Kohlberg's theory, consistently related to role taking opportunities experienced after childhood in adolescence and adulthood. This finding supported Kohlberg's view that moral progress beyond his third stage necessitates contact with other perspectives, namely those of entire cultures or political groups, which individuals are likely to encounter as they become adolescents and adults and thus meet many different people in school and the workplace. Kohlberg and Piaget both emphasized that role taking ability facilitates moral development. Kohlberg argued that cognitive and role taking development are required but not sufficient for moral development. In turn, he maintained that Piaget's cognitive developmental stages underlie Selman's role taking stages, which are subsequently fundamental to his own moral developmental stages. This predicts that cognition develops first, followed by the corresponding role taking stage, and finally the corresponding moral stage, and never the other way around. Conceptually, the three processes have been tied together by Walker. His reasoning is that cognitive development involves the progressive understanding of the environment as it is. Role taking is a step upon this, which is the recognition that people each have their own subjective interpretation of the environment, including how they think about and behave towards other people. Moral development, the final step, is the grasping of how people should think and behave towards one another. Evidence in support of this view comes first from three reviews which showed moderate correlations between Selman's role taking theory, Piaget's cognitive developmental stages, and Kohlberg's moral developmental stages.