The League of Nations Union (LNU) was one among the many organisations, in different countries, that promoted internationalist education among the young in the interwar years. But it was a particularly large and prominent one and appealed to a wide cross-section of teachers and pupils in English schools. LNU junior branches were established in many English secondary schools. These junior branches were part of a wider agenda of active citizenship through extra-curricular means. Their focus was a liberal-internationalist version of "world citizenship" which accommodated existing loyalties to nation and empire as well as loyalty to the wider international sphere. Case studies of junior branches in two girls' schools and two boys' schools draw on school magazines and other sources to shed light on what world citizenship could look like in different school contexts. The traditions and cultures of these different schools, the LNU's ideals and resources, and changing international events, emerge as important shapers of junior branch activities, and responses to these activities. Examining the micro-contexts of junior branches in schools contributes new, grounded, insights to a historiography of internationalist education, indicating ways in which ideals of liberal-internationalist world citizenship were negotiated, promoted, taken up, passed on, altered, and, sometimes, challenged or ignored.