This paper draws on a research study into why more boys than girls choose to study mathematics. My starting point is that only four of the 43 young participants, and all of them male, self-identified as "good at maths". By reading these interviews as narratives of self, I explore the "identity work" accomplished within their talk and within the talk of those who produced themselves/are produced as "not good at maths". I argue that central to this are the ways that young people locate themselves in a series of inter-related gendered binary oppositions including: fast/slow, competitive/collaborative, independent/dependent, active/passive, naturally able/hardworking, real understanding/rote learning and reason/calculation. I then explore the socio-cultural context that makes such imaginings a central feature of young people's relationships with mathematics, discussing the role of the gendered discourses of rationality evident in western enlightenment thinking and in popular culture's stereotypes of mathematical "nerds" and "geniuses". (Contains 3 endnotes.)