Objectives: This study presents processes and outcomes of school-wide positive behavior support (SW-PBS) funded by Seoul Metropolitan Office of Education (SMOE) in South Korea. Methods: The SW-PBS effort has been implemented in six special schools serving students with developmental disabilities. With technical assistance from the SMOE consulting team, these schools organized PBS leadership teams, conducted functional assessment, planned multi-tiered support, implemented universal and individual support, and measured outcomes and fidelity. Results: The SW-PBS efforts resulted in positive behavioral outcomes for students and increased perceptions of efficacy and class management skills for teachers. Conclusions: Future research should continue to examine the effectiveness of SW-PBS and identify the best ways to implement SW-PBS both in special schools and general schools in Korea.