This paper explores gender differential performance in "gifted and talented" 9- and 13-year-olds in a mathematics assessment in England. Boys' and girls' attitudes to mathematics and their views about which gender is better at mathematics are also considered. The study employs the use of a matched sample of boys and girls so that school, age and previous achievement in mathematics can be controlled whilst exploring performance on World Class Test items. The main result of this research was that there was no significant gender difference in performance for the 9- or the 13-year-olds. However, attitudinal differences were found, including a seemingly commonly held stereotypical view of mathematics as a boys' subject. These results are important since the uptake of higher level mathematically-based courses by girls is poor. Further findings reveal that where "gifted" girls perform as well as "gifted" boys, their confidence in the subject is lower than their performance might suggest. This work is also discussed in the light of related research findings and in relation to stereotype threat theory. (Contains 10 tables and 8 figures.)