Teachers play a crucial role as change agents in schools; however, research rarely positions teachers as the implementers of reform. Teachers in classrooms understand the complexity of their context and are well positioned to adapt professional learning to implement change in their schools. Multiple case study, one in Australia and one in Norway was used to investigate the most significant change and the role of social capital in implementing this change. Findings showed when teacher leaders had social capital, they could support colleagues to implement changes in mathematics teaching. This highlights the importance of nurturing networks of teachers' relationships.