This paper reports on research which explored the mathematics teaching efficacy beliefs of preservice primary teachers, where efficacy beliefs describe individuals’ beliefs in their potential to enact teaching to promote learning. Efficacy was conceptualised as a bi-faceted construct consisting of personal efficacy and outcome expectancy. This research sought to establish the extent to which differences in efficacy are explained by students’ mathematics attainment level prior to entry into teacher education; the educational level of the students (whether postgraduate or undergraduate); students’ sense of preparedness to teach mathematics on school placement; and students’ gender. A total of 186 students responded to a questionnaire designed to measure their efficacy beliefs after completing one taught mathematics education module in university and one teaching practice placement in primary schools. Bivariate and regression analysis pointed to complex relationships between the explanatory and outcome variables. On bivariate analysis, findings included statistically significant associations between gender, mathematics attainment, preparedness to teach, and one or both of personal efficacy and outcome expectancy. In the regression analysis, gender was statistically significantly associated with outcome expectancy, while preparedness to teach and mathematics attainment were statistically significantly correlated with personal efficacy. Personal efficacy and outcome expectancy were significantly correlated on bivariate analysis, but significance was not retained after controlling for other factors in the regression models. This research has implications for teacher educators in understanding factors explaining mathematics teaching efficacy and therefore helping to better prepare preservice teachers to teach mathematics in the primary school classroom.