From 1945 to 1975, fifteen Western European countries passed school-leaving age laws that raised the number of years of compulsory schooling for the first time after the Second World War. In order to understand the driving forces behind the increase in compulsory schooling and to explain the timing of this expansion, several areas of research have been reviewed. Economic, political economy and institutional hypotheses have been formulated to explain the passage of the legislation. The results of the estimation of the Cox proportional hazard model are in favour of the modernization theory when the overall period is considered. The 'role of the state' theory performs better until 1970 whereas after the Golden Age, technology and openness appear to be the most important determinants of the expansion of compulsory schooling. Surprisingly, there is no evidence of "contagion effect" in the law's passage.