Within individual countries, the paths toward increasing educational attainment are not always linear, and individuals are not equally affected. Differences between boys' and girls' educational attainments are a common expression of this inequality, as boys are more often favored for continued schooling. This paper examines the importance of birth cohort, sibship size, migration, and school accessibility in explaining both the gender gap and its narrowing in secondary schooling in one district in northeast Thailand between 1984-1994. Birth cohort is a significant explanation for the narrowing of the gender gap. Migration, sibship size, and remote village location are important explanations for limited secondary education opportunities, especially for girls. (Contains 70 references.) (SM)