Figure 2. Girls develop social and complex forms of play earlier than boys, but boys catch up.

Bars and error bars represent percentages (mean + s.e.m.) of children's playtime allocation within social participation categories (girls: dark bars, boys: white bars). No sex differences are found for interactions with adults (a, Adu), unoccupied behavior (b, Uno), onlooker behavior (c, Onl) or parallel play (d, Par). Sex differences appear at some ages successively in solitary play (e, Sol), associative play (f, Aso), cooperative play (g, Cop), and interactions with peers (h, Int). Significant P values are given for Fisher's PLSD post hoc comparisons between girls and boys within age groups. (See also Table S1 for complete descriptive statistics.)