Despite decades of research, little is known about the dynamics of sustaining change in school reform and how the process of change unfolds. By tracing the nine-year reform journeys of four primary schools in Hong Kong (using multiyear interview, observational, and archival data), this study uncovers the micro-processes the schools experienced during their reform. New practices first took root in a group of pilot teachers before gradually disseminating to other teachers and eventually transforming the entire school. Challenges differed across the reform journey. Synergy between school leadership, external support, and organization redesign was critical for initial success. Continued progress depended on whether school leaders and external partners could adapt their roles and redesign the organization to address the school's changing capacity and needs. The study reveals the long-term process of school reform and has crucial implications for policy, research, and practice.