Critical Periods in Child Development and the Transition to Adulthood

Adverse childhood experiences (ACEs) can affect development in ways that disrupt the formation of human capital and contribute to later-life morbidity and mortality. Theories of development predict that the timing of adversity will affect its outcomes. However, empirical evidence for timing-specific effects remains scant. In this issue of JAMA Network Open, Andersen 1 reports an analysis of population-register data from Denmark that suggests timing-specific associations of household dysfunction ACEs with young people's successful transition to adulthood. Andersen's study 1 linked data from several Danish registers to compose records tracking children born between 1987 and 1995 and their families from the child's birth until they reached age 19 years. The analysis tested how exposure to household dysfunction ACEs during ages 0 to 2, 3 to 5, 6 to 12, and 13 to 17 years were associated with disruptions in children's transition to adulthood. Children's ACE exposure was measured from records of parental unemployment, incarceration, psychiatric diagnoses, and divorce as well as children's placement in foster care. Disruption to the transition to adulthood was measured from records of education, employment, criminal charges, and psychiatric diagnoses. Andersen's analysis 1 compared siblings in the same family who experienced household dysfunction ACEs at different stages of development, eg, when a younger sibling's early-childhood exposure was simultaneously their older sibling's middle-childhood exposure. Using this sibling comparison design, Andersen identified a dose-response association between accumulation of ACEs and increased likelihood of experiencing disruption to the transition to adulthood. Adversity exposures during adolescence (ages 13-17 years) had larger magnitude risk associations compared with adversities that occurred earlier in development. Effect sizes for adolescent exposures were nearly 2-fold those for exposures in middle childhood and more than 3-fold those for exposures earlier in life. The findings of stronger associations for exposures during adolescence contrast with the popular narrative of the first 1000 days as a unique window of opportunity to promote positive development. 2 They are also at odds with theoretical estimates from models of dynamic skill formation, which suggest that investments during early childhood should have higher returns than investments later in life. 3 Andersen's results 1 resonate with emerging research streams in both neuroscience and the social sciences to suggest that benefits of interventions in adolescence may be underappreciated. The US Centers for Disease Control and Prevention ACE Pyramid 4 proposes that childhood adversity affects future health through pathways of disrupted neurodevelopment, leading to social and cognitive impairment and the adoption of health risk behaviors. One reason for an early-childhood focus in intervention efforts is the concentration of critical periods in neurodevelopment in the first years of life. 5 However, as Andersen notes, 1 this same logic may also encourage focus on adolescence. New science suggests that adolescence is a second critical period in neurodevelopment, characterized by experience-dependent plasticity affecting higher-order cognitive functions, including memory and self-control. 6 Robust development of these higher-order cognitive functions is essential for a successful transition to adulthood and for health and well-being across adult life. If household dysfunction during adolescence interferes with this development, consequences for the transition to adulthood and beyond may be substantial. Setting aside specific neurodevelopmental vulnerability, adolescence may also be thought of as a critical period in children's human capital development. During adolescence, heightened social sensitivity and increased sensation seeking 7 coincide with tracking into differentiated academic curricula and the first option to drop out of school. Even small disruptions in academic performance can severely reduce access to postsecondary education and future economic opportunities. One