The expansion of compulsory schooling after the Second World War represented an important reform common to the majority of European countries. Specifically, over the period 1950-2000, the fifteen Western European countries considered in this study have extended the school-leaving age by one year or longer. Interestingly, this change in legislation was undertaken by Nordic, Anglo-Saxon and Continental countries, which had different traditions and experiences in educational policy. Many theories have been proposed in the sociology and political science literature to explain the expansion of education during this "period of extensive development of the educational and training system" (Diebolt (1999), p.30). But these country-level studies are too specific to allow any inference on the common factors that may have influenced education policies in a similar way. What is missing in the literature is a comparative analysis of the educational reforms undertaken at the European level. Comparative works by Diebolt and Fontevielle (2001) and Ringer (1979) represent an attractive start but are not sufficient to exhibit the factors driving the expansion of compulsory schooling in general. Nor do they explain the timing and the magnitude of changes in compulsory years of schooling that occurred in most European countries after the war. In contrast, this paper adopts a comparative approach using an original data set for fifteen European countries over the period 1950-2000, and undertakes a quantitative analysis of the determinants of changes in compulsory schooling laws. The major phenomenom the authors observe in the data is convergence: the lower mandatory schooling in 1950, the sooner and the larger the change in the legal age of compulsory schooling. The authors argue that economic forces promote convergence of educational systems for two simple reasons: first, the profitability of education is decreasing at the margin, second, extending compulsory schooling has an increasing marginal cost because years of Secondary are more expensive than years of Primary. In other words, compulsory schooling has decreasing net aggregate returns that trigger convergence. Next, the authors test whether convergence still holds when one controls for other determinants described in the literature. Some theories have emphasized respectively the effects of trade and technological progress, institutional aspects, and constraints set on a benevolent State. They do find conditional convergence as well as evidence supporting some aspects of these theories taken individually. However, the most robust secondary effect is openness: the more open a country, the higher compulsory years of schooling. Rising globalization and public investments into education therefore appear to be complementary phenomenoms in the postwar Western Europe. Appended are: (1) Variables; (2) Tables; and (3) Figures. (Contains 5 tables, 3 figures and 22 footnotes.)