This paper examines the relation between measures of the within-country inequality of student scores on international academic tests and the average level of scores across countries, using the PISA mathematics tests over 2000-2009. It finds that average test scores are higher in countries with lower inequality in scores – a virtuous efficiency-equity relation in test performance – and that family background factors are differently associated with student test performance across countries, but display little impact on the countrywide dispersion of test scores.