Pre-print, Working paper: This paper examines the expansion of compulsory schooling in fifteen Western European countries over the period 1950-2000. We show that a convergence process of mandatory years of schooling has occurred across these countries since 1950. We argue that the major driver of this phenomenom is the existence of diminishing returns to education that limit the extension of compulsory schooling. Then we test whether convergence still holds when one controls for the major three alternative explanations described in the literature, which are respectively based on technology and trade, institutions, and the budget constraint of governments. Conditional convergence does hold and we find that openness, membership of the European Union, urbanization and illiteracy rates are other significant determinants of compulsory years of schooling over this period.