This study extends research on school-based teacher collaboration from single country to comparative settings in Chile and Portugal. Based on interviews with school teachers and principals, the study focused on collaboration engagement and factors conditioning its modalities and depth. Findings indicate that more than country differences and between school differences, collaboration factors and experiences vary according to teacher perception of its value, collective efficacy, school culture/practices and leadership, and in Chile by rural/urban location. Collaboration forms rarely involve more than mutual learning based on sharing of experience. However, involvement in school-based external projects engage teachers in deeper forms of collaboration. Available spaces, time, work-load, systemic policies, testing/accountability are limiting factors.