Democracies invest more in mass education and have higher school enrollment and attendance compared to autocracies, but prior research has not found a positive relationship between democracy and average student achievement. With a focus on students’ learning outcomes and adults’ cognitive abilities, this dissertation expands prior research to examine the nuanced role of political regimes in predicting school quality. Study 1 explores how countries respond to poor student achievement revealed in the Programme for International Student Assessment (PISA). Based on the analysis of PISA scores, both democracies and autocracies react to students’ underachievement by subsequently improving their performance and by increasing public expenditure on schools. Study 2 investigates the subject-specific effects of political regimes on student achievement and argues that, unlike democratic governments, autocrats do not cultivate critical thinking. Employing the largest country-level dataset of students’ learning outcomes, time-series cross-sectional regression analysis shows the positive effects of democracy on students’ scores in subjects that require critical thinking, but not in those that require subjectspecific knowledge. Multilevel analysis of individual-level performance in separate PISA tasks provides more fine-grained evidence that democracy is positively associated with critical thinking abilities even after controlling for students’ socio-economic backgrounds. Complementarily, a qualitative case study of Russia illustrates the mechanisms that can discourage critical thinking under autocratic rule. To go beyond adolescents’ learning outcomes, Study 3 focuses on how political regimes promote adult cognitive skills not only during compulsory schooling but also through higher levels of education. Drawing on large-scale individual-level Programme for the International Assessment of Adult Competencies (PIAAC) data on cognitive skills, cross-sectional regression analysis shows that more education received under democracy predicts better proficiency of adults who advance in their education. Overall, this dissertation enhances the understanding of school quality under distinct political regimes and provides meaningful insights into the role of democracy in promoting cognitive skills through different levels of formal education.