Gender gaps in reading achievement favoring girls are observed consistently across countries and over time, yet the mechanisms underlying changes in these gaps remain insufficiently understood. Psychological explanations often emphasize relatively stable gender differences in cognitive abilities or motivation, but such accounts struggle to explain why gender gaps vary substantially across countries and historical periods (Hyde, 2005). This study investigates whether changes in gender differences in reading behavior are associated with changes in gender differences in reading achievement at the country level, thereby providing evidence for environmentally driven explanations of gender gaps. Using country-level data from six cycles of international large-scale assessments of reading conducted between 1970 and 2016 (Mullis et al., 2017), we examine long-term trends in gender gaps in both free-time reading behavior and reading achievement at the end of primary school. The data combine multiple cross-sectional samples of different student cohorts, allowing us to study within-country changes over time rather than cross-national differences at a single point. Gender gaps in reading behavior and achievement are operationalized as standardized differences between girls and boys. We estimate longitudinal linear models with country fixed effects, thereby accounting for all time-invariant country characteristics such as language, educational traditions, and institutional structures. This modeling strategy isolates within-country variation over time and allows us to assess whether increases or decreases in gendered reading behavior coincide with corresponding changes in achievement gaps. Across model specifications, we find a positive and statistically significant association between changes in reading behavior gaps and changes in reading achievement gaps. Substantively, the estimated effect implies that realistic within-country changes in reading behavior gaps—typically on the order of 0.25 standard deviations—are associated with meaningful reductions in achievement gaps, amounting to roughly 15–20 percent of the average gender gap in reading achievement. These findings are consistent with the Gender Similarity Hypothesis (Hyde, 2005) emphasizing gendered socialization and learning environments. Importantly, while this study does not directly test psychological mechanisms, it demonstrates that gender gaps can change over relatively short historical periods—changes that are unlikely to be explained by genetic or innate psychological factors. The results highlight reading behavior as a malleable, policy-relevant factor and suggest that encouraging boys’ engagement in reading outside school may contribute to reducing gender inequalities in reading achievement, in line with international policy goals on gender equality in education (United Nations, 2015).

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