This paper explores the effect of cross gender relations on the construction of boys' masculine identities. The findings are based on data gathered from a year long empirical study of 10 to 11-year-old boys set in three UK junior schools. Although masculinity is defined against femininity and boys needed to mark out a set of distinctions from themselves and girls, I found that most boys categorized girls as different ("they" are not "us") rather than oppositional, and the most common reaction was one of detachment and disinterest. Rather than maintaining that there are two separate worlds, I argue that there are two complementary gendered cultures, sharing the one overall school world, which are further nuanced by social class and race/ethnicity. Although there was a tendency of boys to dominate space and girls were often excluded from playground games, many girls refused to be dominated by boys, and some were able to deliberately exercise power over them.