Since the publication of the Coleman report in 1966, research on the role of schools in influencing student achievement relative to the role of family background has generated considerable interest and controversy. A large volume of international and comparative research has also been devoted to studying school effects on student achievement. Relatively few studies have examined international differences in the importance of schools in bridging achievement gaps based on socioeconomic status (SES). Using PISA 2012 data, this study examines the role of schools in bridging within-school SES gaps in achievement and compares findings across 61 countries. Contrary to prior research, we find that schools may have limited ability in bridging SES gaps that exist within schools. We also find that across all countries included in the study, specific factors such as the school's learning environment and school context are not systematically associated with within-school SES gaps.