The aim of this study was to explore the relationships between prior knowledge, academic self-beliefs, and previous study success in predicting the achievement of 139 students on a university mathematics course. Structural equation modelling was used to explore the interplay of these variables in predicting student achievement. The results revealed that domain-specific prior knowledge was the strongest predictor of student achievement over and above other variables included in the model and, together with previous study success, explained 55% of the variance. Academic self-beliefs strongly correlated with previous study success and had a strong direct influence on prior knowledge test performance. However, self-beliefs predicted student achievement only indirectly via prior knowledge. The results imply that both prior knowledge and self-beliefs should be taken into account when considering instructional support issues, because they can provide valuable insights about the future performance of the students. (Contains 2 figures and 1 table.)