To examine the role of inequality in academic achievement, we analyse a cross-national dataset including data from three cycles from 2012 to 2018 from the PISA, an international assessment of 15-year-old students' math, reading, and science performance. The Gini coefficient and gender inequality index (GII) were used as metrics for a country's economic inequality and gender inequality, respectively. The results show that gender inequality has a negative association with academic achievement for both boys and girls. Moreover, gender inequality has a stronger association with academic achievement than does economic inequality. We also find that gender inequality in reproductive health may contribute substantially to the association between gender inequality and academic achievement. Despite substantial advances in gender equality worldwide, multisectoral and multilevel approaches from the community to the country level are needed to ensure substantial long-term reductions in economic, gender, and educational inequalities.