Educational systems considerably influence educational opportunities and the resulting social inequalities. Contrasting institutional regulations of both structures and contents, the authors present a typology of educational system types in Germany to analyze their effects on social inequality in eastern Germany after unification. After 1990, the comprehensive secondary school was replaced by three types of differentiated secondary schooling. In this unique field experiment of model transfer and institutional change in a federal country, reforms in these state educational systems—all originally of a uniform socialist type—led to participation rates rising to western enrollment levels, yet with substantial state-level differences. These are attributable to the divergence of educational systems reformed according to contrasting western German models. These types substantially and differentially generate intergenerational inequalities. The authors chart the sharp and significant effects of education policy reforms and societal transformation following German unification.