PGS Browser: a public platform for personalized polygenic score analysis and interpretation.

For many children, pubertal development is not only a biological transition but also a socially consequential one. Youth who mature earlier than their peers often encounter shifts in expectations, social roles, and peer dynamics at a time when many same‐age peers have not yet undergone similar changes. As a result, early‐developing youth may experience a sense of mismatch between themselves and their peer group, which has been linked to a range of behavioral and emotional difficulties (Mendle et al. ; Negriff and Susman ). A substantial body of research has sought to explain these associations by focusing on peer processes, particularly affiliation with deviant peers. Studies consistently show that early pubertal timing is associated with increased likelihood of affiliating with peers who engage in problem behaviors, which in turn is linked to maladjustment (Lynne et al. ; Marceau and Jackson ; Mendle and Ferrero, ; Mendle et al. ; Mrug et al. ; Stepanyan et al. ; Teunissen et al. ; Wang et al. ; Zhu et al. ). For example, Lynne et al. () demonstrated that early‐developing youth who affiliated with deviant peers exhibited elevated levels of aggressive and delinquent behavior across middle school. Despite this emphasis, far less is known about the role of positive peer group affiliation, that is, affiliation with peers who display prosocial characteristics such as kindness, cooperation, and reliability. This omission is notable, given that peer affiliation reflects not only exposure to risk but also access to protective social resources. A growing body of work suggests that affiliating with prosocial peers is associated with lower levels of problem behavior and greater social competence (Busching and Krahe, ; Denio et al. ; Donlan et al. ; Gallardo et al. ; Haddow et al. ; Lansford et al. ; Williams and Anthony ). Thus, understanding how positive peer group affiliation is linked to pubertal development may provide a more balanced account of the social processes surrounding puberty. Importantly, peer affiliation is not random. Rather, it reflects processes of selection and social organization. Youth tend to form relationships with peers who are similar to themselves—a principle known as homophily (Brown, ; McPherson et al. ). In the context of pubertal development, youth who mature earlier or more rapidly may seek out peers who appear more similar in physical development, even if those peers differ in chronological age (Haynie ; Lynne et al. ; Negriff et al. ; Stattin et al. ). These selection processes may shape the peer contexts in which early‐developing youth are embedded. However, similarity may also emerge around behavioral and social characteristics, such as prosociality. From this perspective, peer affiliation may reflect both maturational alignment and shared social orientations.