During the past half-century, there has been a trend toward increasing the minimum age a child must reach before entering school in the United States. States have accomplished this by moving the school-entry cutoff date earlier in the school year. The evidence presented in this paper shows that these law changes increased human capital accumulation and hence adult wages. Backing up the cutoff by one month increases average male hourly earnings by approximately 0.6 percent. The evidence also suggests that the majority of the cohort benefits from backing up the cutoff, not just those who must delay entry. (Contains 2 figures, 12 tables and 32 footnotes.)