The issue of females' lack of participation in high level mathematics at the senior levels of schooling has been one which has caused much debate. In Australia and overseas, females are less likely than males to participate in mathematics and science in the senior years of secondary education. One of the strategies which has been proposed to redress this imbalance has been the use of single sex mathematics classes within the school. The subjects of this study were a cohort of students at four different campuses of one school. At one campus, students were allocated to single sex mathematics classes for Year 10, and then returned to mixed sex mathematics classes in Years 11 and 12. At the other campuses, students were always taught in mixed sex classes. Comparisons were made with students from the other campuses and students from the same campus in other years. The research explored the hypothesis that being a single sex mathematics class would improve the confidence of the female students in Year 10, which would in turn lead to an increase in the participation rate of females in high level mathematics in Years 11 and 12. The findings indicated that the experience of single sex mathematics classes in Year 10 did not enhance the confidence levels. There was no increase in the participation rate in high level mathematics of either females or males from the experimental group. As this group of students was the first at their school to experience single sex classes in a coeducational school, it might be that problems of implementation made the intervention unsuccessful.