After describing both average scores, dispersion, and social inequalities in achievement in the various countries included in the latest Programme for International Student Assessment (PISA) study, this article relates those "products" to country economic and cultural characteristics. It then explores relations between student scores and a number of institutional characteristics of countries' educational systems. Results show that relations exist between average scores and certain institutional or pedagogical practices such as grade repeating or tracking. A high degree of social inequality in achievement proves to be associated with overall score dispersion and degree to which educational system differentiates among students. (Contains 10 notes, 1 table, and 3 figures.)