Influenced by educational, societal and political developments democratic citizenship education in schools has received growing attention since the early 1990s. This has led to formulation of stricter educational policy in many countries, often based on standardized assessment of democratic knowledge, skills and attitudes. But what counts as ‘democratic citizenship’? How should key values like freedom, equality and solidarity be operationalized in educational settings? At which level should this be done and who has the democratic authority to decide on this? Once debate about democratic citizenship moves beyond good intentions and abstract ideas, it becomes a site for political, scholarly and educational contestation. The recent rise of ‘evidence-based’ democratic citizenship education raises questions about democratic citizenship as an educational goal and the role of the educational sciences in educational policy and curriculum making. To better understand and evaluate the current entanglement of educational science and policy making on democratic citizenship education this dissertation provides a historical and comparative perspective. It investigates how democratic citizenship education has been studied scientifically, in interaction with policy and practice, in the United States and the Netherlands over the last hundred years. It presents analyses of theories and practices of democratic education at the experimental schools of Teachers College, New York during the Interbellum; the rise and fall of research traditions in the scientific debate on democracy and education in Pedagogische Studiën since 1920; and the interaction between educational and political discourses in American Civics and Dutch Maatschappijleer textbooks in the second half of the twentieth century.