This paper shows how a significant, but short-lived, episode in Scotland's educational history--the rise and decline of Socialist Sunday Schools (SSSs) in the first half of the twentieth century--provoked controversial debates about issues that continue to have relevance today. The first half of the paper explains the origins of SSSs, their links to adult political groups, the form and content of their meetings, and publications designed to advance their agenda. It also describes the criticisms they received from religious leaders and Conservative politicians, on the grounds that they undermined faith and preached revolution. This leads into the second part, which considers whether SSSs might be regarded as agencies of indoctrination, promoting a version of citizenship that sought to subvert existing institutions and disrupt the social order. It is argued that complete neutrality in educational systems is not possible and that a study of the SSS movement has considerable potential as an educational resource, particularly for teachers of history, politics and social studies.