The main purpose of the study is to analyze whether globally observed trends towards preschool expansion have impacted student achievement in primary and secondary school. We use data from multiple study cycles of two international large-scale assessments that have a longitudinal component at the country level—PIRLS and PISA—and combine these data with a country-level measure of preschool enrollment rates as the main explanatory variable. Employing a multilevel regression with fixed effects for countries and years, we find that changes in preschool enrollment are unrelated to changes in average student achievement. Even after controlling for covariates on the individual and country levels, we do not find any support for the policy expectation that expanding preschool enrollment per se leads to better student achievement on country level.