Research on early compulsory schooling laws finds minimal effects on attendance but fails to investigate heterogeneous effects. Similarly, research proposes limited contexts in which expansion policies can increase equality but has difficulty separating policy and cohort effects. Capitalizing on within-country variation in timing of early compulsory laws, passed 1852 to 1918, I ask whether they improved equality of school attendance or educational attainment by class, nativity, and race. Based on census data, compulsory laws increased equality of attendance and attainment, particularly among young men in the North, where the laws reduced class and race gaps by over 20%. Early compulsory schooling laws provided "hidden gains," missed in previous analyses, suggesting policies that raise minimum schooling can increase educational equality in certain contexts.