Between 2011 and 2015, at the dawn of the global financial crisis, Spain went through severe austerity measures that led to social unrest and to the emergence of new expressions of collective action. In the educational field, teachers' unions and grassroots movements organised against the neoliberal and neoconservative policies promoted by the central government and several regional governments. The case of the Teachers' Assembly in the Balearic Islands is particularly relevant because it was a highly successful protest experience that triggered unprecedented social mobilisation and broad social support. Drawing on social movement theories and combining semi-structured interviews with document and media analysis, this study finds that the combination of alliance-building, disruptive collective actions, and framing processes was key to explaining the success of the social mobilisation.