In this chapter, hierarchical linear modeling is applied to investigate possible gender differences in reading achievement. First, a two-level hierarchical linear analysis is undertaken for each country on each occasion separately. This application of analysis serves to examine the robustness of relationships among variables and to prepare for the subsequent conjunct analysis in which gender differences across countries are examined. The results of the analyses provide evidence with respect to (a) differences in the reading comprehension of female and male students within countries, (b) differences in the reading comprehension of mainly female and mainly male instructional groups within countries; (c) the gender match hypothesis (Elley, 1994; Johnson, 1974) which assumes that students performed at a higher level when taught by teachers of the same sex; and (d) gender differences in reading comprehension between students and between instructional groups across countries. Results of the analyses to elucidate these three issues are presented below.