Since at least the 1980s, motivated, in part, by findings from international comparisons of students' mathematics achievement, some American (U.S.) educators and policy makers have initiated educational reform that focuses on improving teaching practices and curriculum designs by advocating for the adoption of Asian educational models. The implicit assumption behind such reform seems to overlook the possible roles of outside of school factors in superior academic performance in the Asian countries. The purpose of this study was to investigate how outside of school factors were related to students' TIMSS mathematics achievement for the U.S and five top-performing Asian nations or regions, and to examine whether the relative role of school-associated and outside of school factors was consistent across these five Asian countries. The results indicated that students' achievement was highly related to outside of school factors across all six countries. For Singapore and Hong Kong, school-associated factors had somewhat more salient roles than the outside of school factors. However, for Korea, Taiwan, and Japan, school-associated factors played lessor roles in students' achievement performance. As for the U.S., school-associated factors were related to students' performance, however outside of school factors clearly played more salient roles than the school-associated factors. The findings suggest that students' mathematics achievement covaries substantially with outside of school factors. Hence, students' superior mathematics achievement does not necessarily reflect only a superior public school system but also outside of school factors. (Contains 10 tables and 2 figures.)