The purpose of the study was to comparatively investigate student- and school-level factors affecting mathematics achievement of Korean, Japanese and American students. For international comparisons, the PISA 2003 data were analysed by using the Hierarchical Linear Modeling method. The variables of competitive-learning preference, instrumental motivation and mathematics interest were used as student-level predictors on mathematics achievement. The variables of student-teacher relationship and school disciplinary climate were also used as school-level variables. The results of the study showed that different patterns of the relations between student- and school-level predictors and mathematics achievement were present among the three countries. Specifically, the predictor of competitive-learning preference was significant on mathematics achievement in Korea and Japan, but not in the US. For Korean and Japanese students, unexpectedly, mathematics interest was a stronger predictor than was instrumental motivation; in contrast, the pattern was the reverse for American students. For school-level predictors, school disciplinary climate was a significant predictor on the achievement differences in all three countries; however, the variable of student-teacher relationship turned out to be significant only in Japan. Implications of the results are discussed from the comparative perspectives of cultures and educational contexts of the three countries. (Contains 6 tables and 1 note.)