Although researchers have studied children’s peer relationships since the 1930s (Ladd 2005), the end of the twentieth century marked a flurry of psychological inquiry into the impact of peers on development and behavior. Traditionally, adults, especially parents, were considered the primary socializers, responsible for assimilating the child into society. However, according to developmental-ists like Jean Piaget and Willard Hartup, children grow up in two distinct social worlds characterized by different types of relationships—the world of adults and the world of peers. Adult-child relationships are hierarchical, with power residing largely with the adult, whose greater experience and knowledge are essential for socializing the child as a new member of society. Yet peer relationships are also critical, though organized quite differently. Contemporary peer relationships are between age-mates of roughly equal power, operating at similar developmental levels, both cognitively and physically. The egalitarian nature of peer relationships makes them unique contexts for developing skills like negotiation, perspective-taking, cooperation, problem solving, and so on.
Peers can serve as socializers in the absence of adults, as shown in Anna Freud and Sophie Dann’s (1951) studies of peer rearing among children during World War II (1939-1945) and in Stephen Suomi and Harry Harlow’s (e.g., 1972) studies of nonhuman primates. Even when adults are available, however, peer influences are now understood to be significant. Judith Rich Harris has questioned traditional notions of the socialization process, emphasizing the impact of peers and community in her group socialization theory (GST). Using behavioral genetics research that attempts to specify the relative influence of hereditary versus environmental influences, Harris points out that about 40 to 50 percent of one’s personality is attributable to genetics, but only 10 percent or less can be attributed to family and parenting factors, leaving about 40 percent to environmental influences that are unique to each individual. Harris proposes that the peer group is a significant contributor here, challenging us to consider socialization forces beyond the family.
In understanding peer effects, researchers like Wyndol Furman and Philip Robbins (1985) distinguish between the role of dyadic friendships, which fulfill one’s need for intimacy, affection, and reliable alliance, and relations within the peer group, which meet one’s need to belong in a larger social context. Both friendships and peer group acceptance contribute to development across the life span, though their impact may differ. For example, Catherine Bagwell, Andrew Newcomb, and William Bukowski (1998) found that children’s friendships were associated with better attitudes toward family relationships, greater self-esteem, and lower risk for depression more than a decade later in early adulthood. Being accepted by the peer group also predicted later adjustment associated with higher educational aspirations, better school performance, and job success.
At the dyad level, research by Hartup and others has shown that children and adolescents who have friends are more socially competent, report more positive well-being, and exhibit fewer psychosocial problems than children without friends. Having friends seems particularly important in school adjustment, as the presence of friends facilitates initial school entry (Ladd 1990), helps students navigate later academic transitions (e.g., Berndt et al. 1999; McDougall and Hymel 1998), and impacts students’ school engagement and motivation (e.g., Kinderman et al. 1996; Ryan 2000).
The impact of friends can be positive or negative, depending on who those friends are, or rather how they behave. Young people whose friends exhibit antisocial or problem behavior are far more likely to exhibit negative behaviors themselves (e.g., Brendgen et al. 2000). Thomas Dishion and colleagues (1999) have shown that peer "deviancy training" happens subtly, not just through modeling, but through conversational and behavioral rewards (e.g., laughing when peers describe deviant acts they committed). For children who are already at risk for antisocial behavior due to socioeconomic disadvantage or poor family functioning, the likelihood of going down this path appears to be increased by association with deviant friends (e.g., Ary et al. 1999; Fergusson et al. 1999; Kim et al. 1999). In addition, research by Frank Vitaro and colleagues (e.g., 2001) shows that the success of interventions for high-risk youth is enhanced by less association with deviant peers and more association with nondeviant peers who provide alternative role models and support socially acceptable behavior.
In understanding peer effects, it is important to move beyond popular thinking about "peer pressure" as stemming from power based on coercion (e.g., threat of punishment for noncompliance) or rewards (e.g., influencing behavior by controlling rewards). Peer influences can also be indirect, based on referent power (French and Raven 1959), affecting young people’s attitudes and behaviors simply because others admire them and want to be like them or affiliated with them. As Harris suggests, peers do not just "push"; they also "pull."
Perhaps the strongest evidence for peer effects comes from research on peer rejection. Since the 1930s, studies have compared individuals who experience good peer relations with those who are disliked or rejected by peers. This research shows that peer rejection predicts later maladjustment in academic (e.g., poor achievement, school dropout), externalizing (e.g., aggression, criminality), and internalizing (e.g., loneliness, depression) realms (McDougall et al. 2001). To explain the effects of peer rejection, Jeffrey Parker and Steven Asher (1987; see also Parker et al. 1995) propose that deviant social behaviors (e.g., aggression, social withdrawal) often lead to peer difficulties and peer rejection, which in turn places a child at serious risk for a host of poor adjustment outcomes, not only because of opportunities for peer-deviancy training, but also because of missed positive peer-socialization experiences that promote healthy development.
Peer group rejection has also been linked to both poor achievement and school dropout (see Juvonen and Wentzel 1996; McDougall et al. 2001), although the process begins in the early years of school. When Eric Buhs, Gary Ladd, and Susan Herald (2006) followed children through elementary school, they found that early peer rejection affected later school engagement and, in turn, achievement. Children rejected in kindergarten were more likely to avoid school and participated less in class over time, but the outcome depended on the peer treatment received. Rejected children who were abused by their peers were more likely to avoid school. Those who were excluded by peers were less likely to participate, which in turn lead to lower achievement. A critical challenge for educators (see CASEL) as well as parents (see Rubin 2002) is to recognize the interface of peer relationships on academic and life success.
