Poor academic performance during childhood predicts later adverse outcomes, and could be targeted for improvement if detected early. This study used population-based record linkage to examine the association between early life risk factors and academic achievement at two different stages of development using two different cohorts: a kindergarten (~age 5 years) and a grade 3 cohort (~age 8 years). Similar factors were predictive of academic performance in both age groups, including positive effects of increasing maternal age and lack of maternal prenatal smoking. Female sex was associated with higher scores for literacy. The results suggest that children with less developed academic skills can be identified earlier, with effective programmes to enhance academic skills needed during the first year of school to enhance subsequent results.