The Psychosocial Implications of Age Differences between Peers: Insights from School Cohort and Dyadic Friendship Contexts

Differences between people in aspects of identity or presentation, such as gender or ethnicity, may influence interpersonal experiences and social development (Graham et al., 2009; Maccoby, 1990). It is possible that age differences, too, shape the ways in which individuals interact with others or perceive themselves within the social world. This dissertation is composed of two separate studies that together seek to provide greater insight into the ways in which age differences in social contexts may contribute to psychosocial outcomes.
Study I examined relative age differences in a peer group context. Prior work has found that children who are relatively old within a given peer cohort may experience academic and athletic advantages (Barnsley et al., 2020). This study extended the literature by exploring in depth the possibility that relative age in a peer cohort context is also associated with social-emotional outcomes. Contrary to expectations, relatively younger age was found to predict a higher degree of social competence in high school, better social self-concept in adulthood, more romantic relationship satisfaction in adulthood, and fewer depressive symptoms in adulthood. The implications of these counterintuitive but robust findings are discussed in relation to school timing decisions and school policies.
Study II examined age differences in a one-on-one friendship context. Remarkably few studies have sought to characterize consequences of age differences within dyads of peers, though there is some evidence that age differences among friends could affect peer influence processes (Popp et al., 2008). This study extended the literature by investigating the role of age differences between close friends in shaping peer influence processes around drinking and dating behaviors. Findings were mixed: older friends demonstrated greater influence over drinking behaviors between ages 16-17; while regardless of age, all friends demonstrated mutual influence over dating behaviors between ages 15-16. Suggestions for further research in this understudied domain are emphasized, and interventional implications are discussed.
Relative age in a cohort context is a separate construct from relative age in a dyadic context. Therefore, each study has its own literature review and discussion, and are presented sequentially. A general conclusion section comments on take-aways from both studies.