Researchers have long postulated the existence of a big fish little pond effect (BFLPE) where, conditional on achievement level, a student’s academic standing in class or school impacts his or her academic self-concept. Few studies, however, use rigorous causal research designs to identify whether the BFLPE exists. The goal of our study is to use causal research designs to identify the BFLPE and examine whether it differs across national contexts. To accomplish our goal, we analyze cross-national TIMSS 2011 data using cross-subject student-fixed effects models. We provide the strongest evidence to date that a sizeable BFLPE exists in STEM subjects irrespective of national context.