The YDS aimed to examine the consequences of formative experiences in adolescence for mental health, value formation, educational achievement, and multiple facets of behavioural adjustment. As the participants aged, the focus shifted to adult development and attainment and, most recently, mid-life adjustment and health. The initial cohort (G2) was recruited randomly from 9th graders attending the St. Paul (Minnesota) Public Schools in the United States of America in 1988. The parents (G1) and adolescent children aged 11 years and older (G3) of G2 were also assessed. Baseline data collection began in 1988. G2 was followed up every one to two years from 1988 until 2011 and for a final wave in 2019. G1 was assessed in 1988 and 1991. Baseline assessment of G3 began in 2009, and this cohort also completed the final wave in 2019.