Extensive support for the seemingly paradoxical negative effects of school- and class-average achievement on academic self-concept (ASC)-the big-fish-little-pond effect (BFLPE)--is based largely on secondary students in Western countries or on cross-cultural Program for International Student Assessment studies. There is little research testing the generalizability of this frame of reference effect based on social comparison theory to primary school students and or to matched samples of primary and secondary students from different countries. Using multigroup-multilevel latent variable models, we found support for developmental and cross-cultural generalizability of the BFLPE based on Trends in International Mathematics and Science Study data; positive effects of individual student achievement and the negative effects of class-average achievement on ASC were significant for each of the 26 groups (nationally representative samples of 4th- and 8th-grade students from 13 diverse countries; 117,321 students from 6,499 classes).