This article details research into the articulation and implementation of global citizenship education (GCE) in an International Baccalaureate international school. It delineates the perspectives of school community members on contextually specific aspects of GCE and offers a substantive theory of GCE practice in a transnational context. Along with allosyncrasy, denoting the behaviours, propensities, and temperament unique to individuals and groups interrelating with others, the analysis indicates three sub-core categories: authenticating through action, determining empathetic propensity, and enacting long-term responsiveness. These categories are further interpreted against the thinking of David Hansen and Michel Foucault, signifying a break from normative divergence, plurality and individualism. This research will interest those seeking insight into innovative school-based GCE development, practical, cultural convergence, and conceptions of civic action within transnational educational practice.