How children learn to construct and enact masculinities and femininities is clearly an issue for education and one that has been explored in a wide variety of ways. In recent years, however, our conceptions of gender have once again become problematic, particularly given a gradual slippage regarding the sex/gender distinction and the increasing use of 'gender' to refer to matters of biology as well as those pertaining to the social. We now need to rethink how we understand what it is to be male and female, masculine and feminine, and whether the sex/gender distinction and related dualisms are useful to our conceptualization of gender. One way to do this is to focus on the construction of gender in the social systems of which children are a part, including the schooling system. In this paper I consider the legacy of Cartesian dualism both for our understanding of sex and gender and for the schooling system, exploring the interconnections between the two. I examine how the Cartesian legacy underpins the disciplinary and curriculum structures of schools and explore the implications for the ways in which we, as researchers and teachers, view and treat children in schools. Finally, I argue that researchers working in gender and education need to take much more account of the specificities of children's bodies.