The big-fish-little-pond effect (BFLPE), the negative effect of school-/class-average achievement on academic self-concept, is one of educational psychology's most universal findings. However, critiques of this research have proposed moderators based on achievement motivation theories. Nevertheless, because these motivational theories are not sufficiently well-developed to provide unambiguous predictions concerning moderation of the BFLPE and underlying social comparison processes, we developed a Theory-Integrating Approach; bringing together a panel of experts, independently making theoretical predictions, revising the predictions over several rounds based on independent feedback from the other experts, and a summary of results. We pit a priori hypotheses derived from achievement motivation theories against the more parsimonious a priori prediction that there is no moderation based on previous BFLPE empirical research and Darwinian-economic theory (N = 1,925 Hong Kong students, 47 classes, M age = 12 years). Consistent with both BFLPE research and Darwinian perspectives, but in contrast to achievement motivation theory predictions, the highly significant BFLPE was not moderated by any of the following: prior achievement, expectancy-value theory variables, achievement goals, implicit theories of ability, self-regulated learning strategies, and social interdependence theory measures. Although we cannot "prove" that there are no student-level moderators of the BFLPE, our synthesis of social comparison posited in the BFLPE theory and an evolutionary perspective support BFLPE's generalizability. We propose further integration of our Theory-Integrating Approach with traditional Delphi methods, combining quantitative and qualitative approaches to develop a priori theoretical predictions and identify limitations in existing theory as an alternative form of systematic review.