A national network of ten private and comprehensive schools was developed over the last two years. It involves teachers and students working together in order to spread awareness about the Millennium Development Goals in their school communities and in Portuguese society more generally. Evaluating the process, with the support of the High Commission for Immigration and Intercultural Dialogue (ACIDI) and several partner organizations, the practitioners noted several issues regarding student marginalization that emerged. Inspired by the international network’s earlier learning, a new phase of the project started in two schools: a private school and a comprehensive secondary school in the suburbs of Lisbon. This latter school has a strongly diverse population, with a large number of students with an immigrant background. The two schools have carried out an action learning process involving groups of students collecting and analysing data, coordination teams of teachers learning together, and researchers from ACIDI and partner organisations acting as critical friends. This paper focuses on the research carried out by the students in the comprehensive school. It will report on the process of involving and training the students; defining a research focus; collecting and analysing data; and the effects on the school’s development plans.