Institutionalists argue that there are proximate and fundamental causes of economic development. I apply this theory to examine whether national culture is the fundamental cause of student achievement across countries, while family, school, and school system characteristics are the proximate causes of this achievement. I find that national cultural characteristics explain 62% of the variation in PISA average mathematics scores and 50% of PISA reading literacy scores across 59 countries. Family, school, and school system characteristics can explain 60% of the variation in average mathematics scores and 57% of the variation in reading scores, but when both sets of characteristics are included in the analysis, the cultural characteristics explain most of the variation in the scores. This evidence supports the argument that schools function as agents of society and have a limited capability to raise students’ average test scores absent accompanying changes in a country’s cultural characteristics.