This study by Jennifer Watling Neal and colleagues examined classroom friendships in five U.S. elementary schools and describes how boys and girls have no problems being friends together but for some reason have a perception that only boys play with boys and girls play with girls.

From the press release:

“Kids believe gender plays a larger role in friendship that it actually does,” said Neal, assistant professor of psychology.

Children who have more accurate perceptions of the social relationships around them may be better able to avoid conflict and have more positive interactions with their peers, Neal said.

The findings also have implications when the students grow up.

“In adulthood,” Neal said, “we know that people who have accurate perceptions of workplace relationships tend to be perceived as more powerful and have better reputations than their colleagues.”

The study of 426 second- through fourth-graders found gender is still important in the formation of friendships; children were nine times more likely to be friends if they were the same gender.

However, when asked about their friends’ friends, a child was 50 times more likely to believe two classmates were friends when they were the same gender.

“Thus, while gender does matter a great deal in the formation of children’s friendships, children think it is nearly the only relevant factor,” Neal said.

Abstract from the research:

Using social network data, this study examines which features of social and spatial proximity predict self-reported, or “real,” and peer-reported, or “inferred,” relationships among 2,695 pairwise combinations of African American second- through fourth-grade students (aged 7–11). Relationships were more likely to exist, and more likely to be inferred to exist by peers, between pairs of children who were the same sex, sat near one another, shared a positive academic orientation, or shared athletic ability. Sex similarity had a dramatically larger effect on peers’ inferences about relationships than on self-reported real relationships, suggesting that children overestimate the importance of gender in their inferences about relationships. Results were stable across different grade levels in middle childhood and for boys and girls.