This paper examines the impact of compulsory school attendance laws on educational attainment and earnings. The authors use the season of birth as a natural experiment to estimate the effects of these laws, as individuals born in different months start school at different ages due to varying school start age policies and compulsory schooling laws. They find that as many as 25% of potential dropouts remain in school because of these laws. The study also estimates the impact of compulsory schooling on earnings using quarter of birth as an instrumental variable for education. The results suggest that men who are compelled to attend school longer than they desire by compulsory schooling laws earn higher wages, with an estimated return to education of about 7.5%. The findings have implications for the literature on omitted variables bias in estimates of the return to education, suggesting that conventional OLS estimates may be slightly biased downward.This paper examines the impact of compulsory school attendance laws on educational attainment and earnings. The authors use the season of birth as a natural experiment to estimate the effects of these laws, as individuals born in different months start school at different ages due to varying school start age policies and compulsory schooling laws. They find that as many as 25% of potential dropouts remain in school because of these laws. The study also estimates the impact of compulsory schooling on earnings using quarter of birth as an instrumental variable for education. The results suggest that men who are compelled to attend school longer than they desire by compulsory schooling laws earn higher wages, with an estimated return to education of about 7.5%. The findings have implications for the literature on omitted variables bias in estimates of the return to education, suggesting that conventional OLS estimates may be slightly biased downward.