In Brief

Boys will be boys--and girls will be girls--the more time they spend with same-sex peers, a study in the May issue of APA's Developmental Psychology (Vol. 37, No. 3) finds. Not only do preschool-age children tend to self-segregate by sex, but that segregation leads to the development of different sets of social skills, styles, expectations and preferences.

Over time it may actually become harder for children to interact compatibly with children of the opposite sex, say study authors Carol Lynn Martin, PhD, and Richard A. Fabes, PhD, of Arizona State University.

"You become more competent and comfortable in that style of interaction," says Martin, "and so it's a mutually reinforcing cycle that continues." Preference for sex-segregated play begins at around 2-and-a-half for girls and 3-years-old for boys. By 3- to 4-years-old, in preschool settings, the majority of both boys' and girls' social interactions are with members of the same sex.

The study's sample included 61 children (28 boys and 33 girls) ages 3 to 6 at a university daycare facility. Using what Martin called a "snapshot approach," a picture of the behavior of each individual child in the study emerged by compiling a series of 10-second observations. Nearly 20,000 observations were collected over the course of the study, which lasted six-and-a-half months. "The best picture we got of stability was when we put together a lot of these snapshots," she says. Martin and Fabes found that sex segregation is very strong and moderately stable over time. "In just a few short months, we were seeing the effects of children's same-sex play," says Martin. Girls tend to be encouraging and supportive, she notes. They tend to play indoors and near adults. They play house and other games that require more verbal interaction. "Girls tend to be pretty cooperative with each other," she says.

"Boys are more concerned with dominance and who's in charge, who's the boss." They like rough-and-tumble games and play outdoors. Super-hero play is a common game.

These stereotypical behaviors and tendencies were not universal, however.

"This finding, the effectiveness of peers on children's behavior, wasn't consistent across all children. The more children play with same-sex peers, the more we saw those effects on them," Martin says. She calls this "the social dosage effect."

Though children spend a lot of time playing with same-sex peers (and little with other-sex play partners), they also spend a significant amount of time playing with both girls and boys in mixed-sex groups, Martin says. "Are there advantages to playing with mixed-sex groups and playing with the other sex?" asks Martin. "There is something positive about being comfortable with a variety of interaction styles."