While the literature on the social development of children has increasingly stressed the importance of peer relationships, little research has examined the influence of peers in sex role development. Sex segregation in children's play from preschool through the elementary years remains the norm even though we live in a society that is increasingly sex integrated and that requires social ease between men and women. Unfortunately teachers and parents too easily dismiss the need for both sexes to play together and to get to know each other. Teachers can increase pupils' cross-sex interaction by clearly labelling all play and learning activities as appropriate for both sexes, using mixed-sex small group activities frequently, praising children's positive cross-sex communication, and intervening to reduce cross-sex exclusion, cruelty, or teasing. They can also increase students' understanding about gender and behavior by teaching about sex role stereotypes and sexual and cultural differences in communication patterns. Finally, they can reinforce in all children behaviors usually stereotyped as belonging to one or the other sex, and make certain that all children have leadership roles and the chance to carry out and observe prosocial behaviors. A 34-item reference list is included. (IS)