Final answer:
Piaget and Kohlberg extensively wrote about the development of moral reasoning.
Step-by-step explanation:
The researcher who wrote most extensively about the development of moral reasoning is Piaget and Kohlberg. Lawrence Kohlberg, who built upon the work of Jean Piaget, proposed a theory of moral development that consists of three levels: preconventional, conventional, and postconventional. Kohlberg's theory suggests that individuals progress through these stages as they mature, with each stage representing a higher level of moral reasoning.