Family background is known to have a substantial impact on students’ literacy and numeracy results. This raises questions about whether any of the remaining differences in results are due to school performance – or whether they are merely due to random noise. This article reviews research from the OECD’s Programme for International Student Assessment (PISA) study, based on student-level analysis. It then presents new evidence based on publicly reported school-level data from Western Australia. Combining test results with data on schools’ socioeconomic characteristics, this study estimates the degree to which some schools outperform those with similar characteristics. On a ‘like schools’ basis, school differences are shown to be persistent across subjects, grades and years.