This paper adopts the stratification-standardization framework proposed by Allmendinger (1989) to analyze the effects of educational institutions and the organization of education on the inequality of opportunity and effectiveness of national education systems. The analyses are conducted on OECD countries participating in the Programme for International Student Asssessment (PISA) 2003 study (OECD, 2004c). The results indicate that educational stratification increases inequality of educational opportunity, while in general, standardization enhances equality. Stratification does not improve overall student performance, and the association between standardization and effectiveness is not straightforward. The most policy-relevant finding is that the early age of selection links closely with high inequality of opportunity. (Contains 13 tables, 3 figures, and 7 notes.)