Between-school differences account for less than 15% of the OECD average total variation in performance in Denmark. By contrast, across OECD countries, 37% of the overall performance differences are observed between schools. The performance differences that do exist between schools are relatively closely related to socio-economic disparities between schools. Performance differences within schools are around the OECD average, but these within-school differences are more strongly related to students’ socio-economic status: 65.8% of the total variation in performance is observed within schools (OECD average: 63.3%), and 10.5% of the performance difference can be explained by differences in students’ socio-economic status (OECD average: 5.1%). In the PISA 2012 mathematics assessment, students with an immigrant background scored an average of 40 points lower than their native peers after accounting for socio-economic background (OECD average: 21 points). Students with an immigrant background in Denmark were 2.43 times more likely to perform in the bottom quarter of the performance distribution than non-immigrant students (OECD average: 1.70 times more likely).