Beginning at an early age, socialization in the family is supplemented by experiences in the wider world of peers, media, and school. In all human societies, children spend many hours in one another's company. Experiments with rhesus monkeys reveal that peer interaction is a vital source of social competence.

Peer sociability begins in infancy, as isolated smiles, gestures, and babbles evolve into coordinated interaction. During the preschool years, cooperative play increases. In middle childhood and adolescence, gains in communication skills and greater awareness of social norms contribute to advances in peer interaction. Parents influence young children's peer relations by arranging peer-play activities and teaching and modeling effective social skills. Cultural values and beliefs about the importance of play influence children's interaction and play activities.

Peer acceptance is a powerful predictor of long-term psychological adjustment. Children's social behavior is a major determinant of peer acceptance. A particularly destructive form of interaction that emerges during middle childhood is peer victimization. By the end of middle childhood, peer groups form, through which children and adolescents learn about the functioning of social organizations. Children socialize one another through reinforcement, modeling, and direct pressures to conform to peer expectations.

American children spend more time watching TV than they do in any other waking activity. Heavy TV viewing promotes aggressive behavior, indifference to real-life violence, a fearful view of the world, ethnic and gender stereotypes, and a naive belief in the truthfulness of advertising.

Computers have become increasingly common in the lives of children. Computer-assisted instruction, word processing, programming, and electronic communications each offer unique educational benefits. Although speed-and-action videogames foster attentional and spatial skills, violent videogames promote aggression and desensitize children to violence. The Internet may enhance understanding of other cultures, but excessive home use negatively affects emotional and social adjustment.

Schools are powerful forces in children's development. Pupils in traditional classrooms are slightly advantaged in achievement; those in open classrooms are more independent, tolerant of individual differences, and excited about learning. Teachers who are effective classroom managers and who provide cognitively stimulating activities enhance children's involvement and academic performance. Educational self-fulfilling prophecies are likely to occur when teachers emphasize competition and comparisons between pupils, have difficulty controlling the class, and engage in ability grouping. To be effective, mainstreaming must be carefully tailored to meet the academic and social needs of children with learning disabilities. Largely due to pressure from parents, some schools have extended mainstreaming to full inclusion.

Regardless of students' abilities, parent involvement in education is crucial for children's optimum learning. Cross-national comparisons of mathematics and science achievement reveal that students in Asian nations are consistently among the top performers, whereas Americans score no better than average and often below it; these differences become greater with increasing grade. American adolescents have no widespread vocational training system to assist them in preparing for challenging, well-paid careers.