This study presents 3 case studies that examine the processes involved in the professional growth of physics teacher-leaders (TLs) in a national network of professional learning communities (PLCs). This program has been operating since 2012, using a "Fan Model" where the TLs participate in a PLC (TL-PLC) led by a team from the Weizmann Institute of Science, while they simultaneously teach in high school and lead nationwide regional PLCs of physics teachers. The context of the study was inquiry-based laboratories, which are aimed at integrating aspects of authentic research into the high-school physics laboratory. The Interconnected Model of Professional Growth (Clarke and Hollingsworth, Teaching and Teacher Education, 18:947-967, 2002) was extended, adjusted to physics TLs, and used to study the processes involved in the growth of the 3 case studies within different aspects of their practice. Changes in their knowledge, attitudes, and practice, as well as the factors that motivated, contributed to, or inhibited their professional growth, were studied over the course of 3 years. Individual growth pathways were found in each case, as well as similar patterns for all 3. The TL-PLC served as an interactive and supportive learning environment, and the mechanisms of "Enactment" and "Reflection" promoted changes in the TLs' knowledge, attitudes, and practice. Addressing challenges such as students' difficulties as well as PLC teachers' motivation and attitudes enhanced the TLs' growth as teachers and as PLC leaders. The findings suggest that PLC programs can serve as an effective framework for the professional growth of TLs, as well as for promoting reform initiatives in science education.