In scaled-up professional development (PD) programs, PD sessions are often moderated by PD facilitators who were not involved in the design process. PD materials are designed to support facilitators’ planning and enactment. Facilitators’ uses and adaptions of PD materials substantially shape teachers’ professional learning opportunities. We report on a 13-year design research study that intertwines design-based research and research-based (re)design of materials, using qualitative insights into adaptation practices and their underlying rationales so that they become adaptable to different contexts while robustly sustaining the program’s core in high-quality enactment. In three design experiment cycles, guidelines for increasing the robustness of materials were developed, focusing on explications of content, goals, and structure. Expert facilitators’ adaptations also promoted the content quality development, especially with regard to integrating theoretical and practical goals. The paper extends the design research methodology to the educational ecosystem into “design research from the facilitation perspec-tive of teacher PD”