The ascendance of economic globalization, epitomized for the United States, Canada and Mexico by the North American Free Trade Agreement (NAFTA), has been paralleled by the increasingly transnational scale of education policy. While national and regional governments remain the employers of public school teachers, the policies articulated by supranational institutions including the Organization for Economic Cooperation and Development (OECD) are ever more influential. Teacher internationalism has become increasingly significant for its capacity to both articulate shared analyses of the predominantly neoliberal character of global education policy, and to coordinate cross border solidarity. The Trinational Coalition in Defense of Public Education emerged in the context of the end of Cold War labor politics, and the signing of NAFTA in 1994. It has become an enduring network of established and dissident teachers’ unions and movements in Mexico, Canada and the US. This article assesses how the Trinational has confronted critical issues for labor internationalism. These include navigating national and international union tensions, facilitating grassroots cross border radical unionist networks,ho rizontal power relations in North-South alliances, moving beyond rhetorical declarations to practical action, and the long term sustainability of international solidarity.