There are relatively few studies in Australia and South-East Asian region that combine investigating models of math growth trajectories with predictors such as reasoning ability and reading comprehension skills. Math achievement is one of the major components of overall academic achievement and it is important to determine what factors (especially domain-general factors) predict levels of achievement over time. This study presents large-scale data (N = 5,886) from Australia to examine the trajectories of growth in math achievement and how problem solving (PS) ability and reading comprehension (RC) skills predict this growth among government school students (grades 3-8) in Victoria. Latent growth modelling showed that PS ability predicts growth in math achievement and this relationship is partially mediated by RC skill. Both PS ability and RC skill predict initial status in math achievement, but only PS ability predicts growth. The data also fit a model in which an improvement in general reasoning ability of students allows those with lower initial levels in math achievement to catch up. This can be interpreted as evidence that improving growth rates in PS ability may lift growth rates in math achievement.