At a time when Australia's international competitiveness is compromised by a shortage of skilled workers in Science, Technology, Engineering and Mathematics (STEM) related careers, reports suggest a decline in Australian secondary school students' performances in international tests of mathematics. This study focuses on the mathematics performance of students in the first year of secondary school and in particular the impact, if any, that the move to secondary school has on this performance. Utilising current state differences in the structure of schools and population data, the study identifies a small effect associated with the transition to secondary school that is comparable to similar international studies. It then explores this effect through a multivariate analysis of data from the Longitudinal Study of Australian Children (LSAC). Results suggest that even after controlling for known predictors of mathematical performance, the transition from primary school to secondary school is associated with a small effect that is not apparent when students change from one primary school to another. These findings confirm a number of qualitative studies that suggest the need for a closer focus on the early secondary mathematics classroom. Implications for researchers and policy makers are also discussed.