In this study, we systematically unpack relationships among student socioeconomic status (SES), science and mathematics achievement, and student interest in science in the context of varying school socioeconomic composition. Using the most recent Programme for International Student Assessment dataset for Australia, we found that increases in school SES are consistently associated with substantial increases in science and mathematics performance. This pattern of association held for all groups regardless of their individual SES. However, our findings also show that students’ interest in science was not associated with varying school SES, and only marginally and inconsistently associated with individual SES. We discuss policy implications and strategies for mitigating the influence of school socioeconomic composition on science and mathematics performance, and for the achievement of more equitable and effective educational outcomes generally.