Canada, the Netherlands, and the United States differ in their social safety nets, education and labour market systems. This dissertation explores how these differences impact adolescent mental health and entry into higher education and work. The dissertation used population-level cohort data of individuals spanning adolescence to young adulthood. Findings show that across the three countries, adolescents exhibit consistent mental health patterns—with most experiencing low symptom levels over time but some experiencing increasing and/or decreasing symptom frequency—that may be related to physiological and social changes during the transition to adulthood. Higher levels of mental health problems at any point in adolescence are associated wit...