This study was to examine the big-fish-little-pond effects (BFLPE) on mathematics achievement by the students' positive attitude toward mathematics (PATM) of Taiwanese eighth-grade students in the Trends of International Mathematics and Science Study (TIMSS). The SLM (students like learning mathematics), SVM (students value mathematics), and SCM (students confident in mathematics) have been three critical factors of students' PATM. The sample comprised 5,042 Taiwanese eighth-grade students from 150 schools that participated in the TIMSS. The two-level hierarchical linear model analysis extends the BFLP positive association between students' individual mathematics achievement with SCM to include SLM and SVM levels. In addition, the BFLPE "negative" correlations between school-average mathematics achievements and aggregated self-concepts have also been confirmed with these three variables. The interaction study indicated that students with high achievements experienced a greater BFLPE on SLM and SCM scores than did students with low achievements. Implications of the findings and suggestions for future study are discussed.