Peer effects on children: What does evidence really show?

Parents often worry about their children’s peer environments, especially when classmates have a reputation for poor ­academic performance or problematic behavior. But how much do these influen­ces truly shape long-term outcomes such as education, ­career trajectories, or economic well-being? These questions are at the center of a ­discussion led by Jacobs Center ­researchers Prof. Manuel Eisner, Prof. Ana Costa-Ramón, and Prof. Ulf Zölitz.

When asked whether parents’ concerns about “wrong friends” are simply prejudice, Ana Costa-Ramón, Assistant Professor of Economics of Child and Youth Development at the Jacobs Center, notes that research consistently shows that disruptive peers can shape children’s long-term outcomes. She explains that even the indirect effects of disruption, such as contact with classmates exposed to domestic violence, leave measurable marks on later behavior and earnings. While the exact size of these effects is difficult to isolate, she stresses that “the pattern is clear – peer environments matter in the long run.”
Ulf Zölitz, Associate Professor of Economics of Child and Youth Development at the Jacobs Center, adds that adolescence is a phase of heightened social sensitivity. Young people, he explains, are exceptionally tuned into their peers, which is why peer characteristics influence not only academic outcomes but also personality development. He explains that peers play a significant role in shaping long-term outcomes such as educational achievement, college attendance, major choice, and even future earnings. But Zölitz stresses that what truly matters is not only the absolute quality of one’s peers but also the adolescent’s relative position within the group. These “rank effects,” he argues, help explain why peer influence can pull young people in different directions. An average student placed among weaker peers often gains confidence and performs better, whereas the same student surrounded by high achievers may feel discouraged and reduce effort.

In discussing the effects of delinquent peers specifically, Manuel Eisner, Wolfson Professor of Criminology at the University of Cambridge and founder of the long‑running z‑proso study at the Jacobs Center, explains that the long-standing question of whether adolescents simply seek out delinquent peers or are actively influenced by them now has a clear empirical answer: “There is a genuine causal effect.” Delinquent peers can do more than reflect a young person’s existing tendencies; they can amplify problematic behavior. Research on youth gangs shows that joining such groups increases both the likelihood of offending and the severity of the offenses. Eisner adds that some adolescents are more easily influenced than others: Those who care deeply about peer admiration are more strongly affected, whereas more inwardly-oriented teens tend to resist group pressure. He also notes that the impact of peers shifts with age. Certain stages of adolescence make young people especially open to what their peers are doing. Evidence shows that moving disadvantaged children to better neighborhoods can help when they are young, but doing so during adolescence may backfire, particularly if the new environment makes them feel that they are at the bottom of the social hierarchy.

Competition is another important dimension of peer influence during adolescence. According to Manuel Eisner, competition often extends beyond school per­formance into less healthy areas, including risk-taking behaviors. However, he notes that competition does not replace cooperation; the two often exist side by side as part of everyday peer interactions. 

Competition does not affect all adolescents in the same way. As Costa observes, competitive settings often place greater demands on girls, a pattern that cannot be fully explained by differences between single-sex and mixed-sex schools alone. Zölitz agrees that girls may feel competitive pressure more intensely, while pointing out that moments of heightened stress, such as school transitions, are usually short-lived and not something to avoid entirely: “The solution is not to avoid all stressful situations.” Appearance-based comparison stands out as especially sensitive. Drawing on z-proso findings, Eisner describes physical attractiveness as a very competitive field for adolescents, closely tied to poorer mental health among those who see themselves as less attractive. He also points out that school structures strongly influence adolescents’ social circles. In tracked systems, “the environment selects for you who you can associate with,” and z-proso data show that gaps in interpersonal trust widen between ages 15 and 24, especially for those coming from more disadvantaged school settings.

Peer support holds a distinct place in adolescents’ lives, offering what Ulf Zölitz describes as a “horizontal orientation” that shapes everyday norms around behavior, risk-taking, and engagement at school, while families provide a more stable and unconditional safety net in the background. Ana Costa emphasizes that it remains difficult to say whether peers or parents matter more overall, as the evidence is far from conclusive. Addressing this complexity, Manuel Eisner notes that long-term z-proso findings consistently highlight the importance of parental involvement, especially meaningful time spent together, over specific parenting techniques or reward and punishment strategies. However, Costa and Zölitz point out that expectations for parental involvement have risen sharply in recent decades, raising questions about the “marginal value” of additional parental time and the risks of very intensive or “helicopter” parenting, which can limit adolescents’ independence. Eisner suggests thinking of the family as a stable, long-term scaffold that provides continuity and support; peers play a more dynamic and increasingly influential role as children move through adolescence.
As teens become more independent, friends often start to play a bigger role in their lives. Manuel Eisner and Ulf Zölitz both emphasize that supportive peer relationships can make a real difference during this period. Eisner identifies having trusted friends in adolescence as “hugely important,” pointing out that this is a key stage for developing identity, independence, and social networks. Zölitz agrees, noting that peers can act as an informal source of support when young people face stress at home, even if this role is not always easy to measure. Supportive friends who listen and show understanding can help adolescents cope with challenges such as illness in the family, financial strain, or conflict at home. Evidence from z-proso helps explain why these connections matter: When young adults reflect on their hopes for the future, they most often mention close social relationships rather than career or income. This suggests that peer connections are key social and emotional resources that may help protect well-being during times of stress. Supporting this interpretation, z-proso evidence from the COVID-19 pandemic shows that young people with stronger social connections coped better with lockdowns.

Peer groups play an important role in shaping bullying, risk-taking, and other delinquent behaviors, so a key question is how the group dynamics operate. Manuel Eisner notes that the influence of delinquent peers is well established, pointing to mechanisms such as imitation, peer-based reinforcement of what is considered cool, status competition within problematic groups, and simple exposure to situations in which misconduct becomes more likely.
Ana Costa is involved in work on the long-term impacts of the randomized KiVa anti-bullying intervention in Finnish schools. Linking trial data for around 15,000 pupils in grades 7–9 to administrative records in adulthood, the study shows that treated students are more likely to enroll in an academic high school, obtain a university degree, and earn higher wages by ages 27–29, regardless of gender or social role at baseline. The findings point to reduced classroom bullying, particularly among boys, as the main mechanism. Lower levels of criminal behavior among boys in adulthood suggest effects that extend beyond the intervention period.

Ulf Zölitz observes that the idea of deliberately engineering peer groups to reduce bullying is appealing, but currently difficult to achieve in practice. Eisner emphasizes that peer dynamics are also shaped by broader social and economic contexts; alternative pathways to status can make delinquent groups appealing. He further notes the importance of adults beyond the family: Evidence from z-proso shows that feeling supported by a teacher can have long-lasting positive effects on behavior, confidence, and educational skills. Both Zölitz and Eisner stress that affective responses depend on the quality of support available in schools rather than class composition alone.

The discussion of peer influence benefits from broader perspectives. Ulf Zölitz points to developmental psychology as especially useful for understanding how peer relationships shape behavior and to neuroscience for insights into why social approval and comparison become so powerful in adolescence. Manuel Eisner stresses that peer influence must be seen within wider social and historical contexts; it is shaped by political, technological, and cultural changes that affect how families, schools, and peers interact across generations. Ana Costa notes that this makes peer research an inherently cross-cutting field that already draws pro­ductively on multiple disciplines.

Taken together, the discussion underscores that peer influence is an important but flexible force in young people’s lives. Peer relationships can introduce risks, but they can also provide support, motivation, and a sense of belonging. What peers ultimately mean for young people depends on the environments they grow up in and how families, schools, and communities shape the spaces in which those relationships develop.

Author:  Marta Dobrijevic
Editor:  Sandro Fässler