This paper assesses two approaches to the measurement of educational inequality in international comparisons between countries and over time. We analyse reading literacy performance of 15-year-old students using data from PISA 2009 and 2015 for 37 EU and OECD countries. We show that inequality of outcome and inequality of opportunity do not necessarily co-vary; they can go in opposite directions both across countries and over time. Our results suggest that indicators of variation in educational outcomes are more suitable to the types of problems that affect international comparisons of educational achievement than the more common approach of measuring of inequality of opportunity.