Research on gene–environment interactions in education focuses on two main hypotheses: the compensatory advantage hypothesis, holding that genetic disadvantage would be less consequential in resource-rich environments, and the Scarr–Rowe hypothesis, based on the idea that the availability of resources can reinforce a genetic advantage. Although regression approaches frame these as mutually exclusive, the underlying theoretical expectations concern differences at the extremes of the genetic distribution, as measured by a polygenic index (PGI). Here compensation and reinforcing dynamics are mapped to socioeconomic (SES) differences in the rate of overachievers (low-PGI individuals who attain a degree) and underachievers (high-PGI individuals who do not). Using three representative datasets from the US and UK, the findings show that compensatory and reinforcing dynamics can operate simultaneously: high-SES students are more likely to overachieve despite a low PGI - suggesting compensation - and less likely to underachieve - supporting Scarr-Rowe hypothesis. This framework challenges the presumed trade-off between equity and efficiency, and, in reconciling longstanding hypotheses on GxE interactions, possibly explains inconsistent findings from the literature.