This paper examines the impact of compulsory schooling laws on educational attainment and earnings using the season of birth as an instrumental variable. The authors find that individuals born in the first quarter of the year tend to have lower educational attainment than those born later in the year due to differences in school start age policies and compulsory attendance laws. These laws require students to remain in school until their 16th or 17th birthday, which means students born earlier in the year may drop out earlier than those born later in the year. The authors estimate that up to 25% of potential dropouts remain in school due to these laws. Using quarter of birth as an instrument for education in an earnings equation, the authors find that the return to education is remarkably close to the ordinary least squares (OLS) estimate, suggesting little ability bias in conventional estimates. The results also imply that individuals compelled to attend school longer than they desire by compulsory schooling laws reap a substantial return for their extra schooling. The authors also find that the seasonal pattern in education is not evident in college graduation rates or graduate school completion rates, suggesting that the relationship between years of schooling and date of birth is entirely due to compulsory schooling laws. Additionally, they find that students born in states with a 16-year schooling requirement are more likely to drop out of school than those in states with a 17-year requirement. The authors use two-stage least squares (TSLS) estimates to analyze the impact of compulsory schooling on earnings. They find that men who are forced to attend school by compulsory schooling laws earn higher wages as a result of their increased schooling. The estimated return to an additional year of schooling for those compelled to attend school by compulsory schooling laws is about 7.5 percent, which is hardly different from the OLS estimate of the return to education for all male workers. The authors also explore the relationship between earnings and season of birth for the subsample of college graduates. They find no relationship between earnings and season of birth for men not constrained by compulsory schooling requirements, suggesting that the TSLS estimate of the return to education reflects the effect of compulsory school attendance. The authors conclude that compulsory schooling laws increase educational attainment for those covered by the laws and that students who attend school longer because of compulsory schooling receive higher earnings as a result of their increased schooling. The findings have important implications for the literature on omitted variables bias in estimates of the return to education.This paper examines the impact of compulsory schooling laws on educational attainment and earnings using the season of birth as an instrumental variable. The authors find that individuals born in the first quarter of the year tend to have lower educational attainment than those born later in the year due to differences in school start age policies and compulsory attendance laws. These laws require students to remain in school until their 16th or 17th birthday, which means students born earlier in the year may drop out earlier than those born later in the year. The authors estimate that up to 25% of potential dropouts remain in school due to these laws. Using quarter of birth as an instrument for education in an earnings equation, the authors find that the return to education is remarkably close to the ordinary least squares (OLS) estimate, suggesting little ability bias in conventional estimates. The results also imply that individuals compelled to attend school longer than they desire by compulsory schooling laws reap a substantial return for their extra schooling. The authors also find that the seasonal pattern in education is not evident in college graduation rates or graduate school completion rates, suggesting that the relationship between years of schooling and date of birth is entirely due to compulsory schooling laws. Additionally, they find that students born in states with a 16-year schooling requirement are more likely to drop out of school than those in states with a 17-year requirement. The authors use two-stage least squares (TSLS) estimates to analyze the impact of compulsory schooling on earnings. They find that men who are forced to attend school by compulsory schooling laws earn higher wages as a result of their increased schooling. The estimated return to an additional year of schooling for those compelled to attend school by compulsory schooling laws is about 7.5 percent, which is hardly different from the OLS estimate of the return to education for all male workers. The authors also explore the relationship between earnings and season of birth for the subsample of college graduates. They find no relationship between earnings and season of birth for men not constrained by compulsory schooling requirements, suggesting that the TSLS estimate of the return to education reflects the effect of compulsory school attendance. The authors conclude that compulsory schooling laws increase educational attainment for those covered by the laws and that students who attend school longer because of compulsory schooling receive higher earnings as a result of their increased schooling. The findings have important implications for the literature on omitted variables bias in estimates of the return to education.