In this article, we focus on the teacher educator’s role in school-based competence development by asking: How can the teacher educator contribute to professionalization from within? The term “professionalization from within” describes how teachers and school leaders should be complementing governmental development strategies by actively pursuing local school development, managing norms and standards, and developing a local, professional knowledge base. The article presents a study based on data from a four-year action research project at a Norwegian primary school where Lesson Study (LS) was put into use as a vehicle for school-based competence development. Through the research question “How did teacher educators contribute to professionalization from within?” and the use of open coding in the constant comparative analysis method (Strauss & Corbin, 1998), three main categories were developed: emotional support, organizational support and process support. “Emotional support” shows teacher educators empowering the practitioners as owners of the development work, appreciating their knowledge and work, inviting them to cogenerative learning and challenging them in supportive ways. “Organizational support” shows teacher educators cooperating with school leaders to establish predictable but flexible structures and leadership for holistic school-based competence development. “Process support” shows research and process-oriented teacher educators contributing to the development of collective research and development skills and strengthening the learning and development processes by introducing LS and other process tools and by combining internal knowledge, research and external knowledge. Mirrordata, collective analysis, theorization and meta-communication are key elements in all three categories.