The occurrence and timing of major demographic decisions in the transition to adulthood is strongly stratified, with young adults with a high socio-economic status (SES) background usually experiencing many of these events later than young adults with a low SES background. To explain this social stratification, we outline a theoretical framework in which social stratification affects choice in the transition to adulthood through three, potentially reinforcing, pathways: stratified socialization, stratified agency, and stratified opportunity. We test our framework against longitudinal data from two waves of the Generations and Gender Surveys for Austria, Bulgaria, and France. We find evidence for the importance of all three pathways. Furthermore, processes differ little by gender, age and country context.