This paper investigates whether school socioeconomic composition has a stronger association with standardized test scores among lower-socioeconomic status (lower-SES) students than it does among higher-SES students. School socioeconomic composition, measured here as average SES, has repeatedly been demonstrated to have a strong influence on a variety of student outcomes, but there has been little systematic examination of whether this association is stronger for more disadvantaged students. Such a finding would be consistent with evidence from related research areas suggesting that the learning outcomes of disadvantaged students are particularly sensitive to schools and school characteristics. We use data from a large, cross -national study—the Programme for International Student Assessment (PISA)—to examine patterns across a wide variety of economic, demographic, and cultural contexts. Contrary to expectation, we find no general pattern of school socioeconomic composition being more strongly associated with test scores among lower-SES students; if anything, the relationship appears to be slightly weaker among lower-SES students.