By comparing two federal education systems, namely Germany and the U.S., and their reactions to PISA we show how international, large-scale student assessments (ILSA) have been used by national stakeholders to gain leverage for legitimising or de-legitimising policy reforms in education. From a neo-institutionalist perspective we argue that country-specific path-dependencies and policy legacies, such as different systems of power devolution, testing traditions and also non-governmental actor influence, additionally moderate the impact of ILSA.