AP Psychology Practice Test 2026 - Free AP Psychology Practice Questions and Study Guide

The study of psychosocial development across the lifespan is primarily attributed to Erik Erikson. Erikson proposed a theory consisting of eight stages that individuals go through from infancy to late adulthood, each characterized by a specific psychological conflict that must be resolved. His stages emphasize the importance of social relationships and the development of identity throughout different periods of life, highlighting how experiences in earlier stages can influence later development. This framework has been instrumental in understanding both individual growth and societal influences on personality and behavior.

In contrast, the other figures listed focus on different aspects of development. Lawrence Kohlberg is known for his work on moral development, particularly the stages of moral reasoning. Jean Piaget concentrated on cognitive development in children, outlining how thinking evolves as children interact with their environment. James Marcia is recognized for his research on identity development specifically during adolescence, which builds on Erikson's concepts but does not encompass the entire lifespan. Therefore, Erikson is indeed the most fitting choice for the study of psychosocial development across all stages of life.