Research on welfare state regimes and research on educational policy share a common concern for the reduction of social inequality. On one hand, welfare state research is typically designed within a comparative approach where scholars investigate similarities and differences in social institutions across selected countries. On the other hand, the basic model of educational policy research is usually country specific and seldom identifies why and how we are to understand cross-national differences pertaining to social inequality. The goal of the research is to bridge these two areas by testing socio-economic gradients and educational outcomes among 15 industrialised countries (using 2003 PISA data) from a welfare state perspective. Results support Esping-Andersen's "three worlds" typology in that the level of between-school educational inequality is the highest in conservative welfare states and is the lowest in social-democratic countries. (Contains 4 tables and 1 figure.)