Sufficiency Economy Philosophy (SEP) is an approach used to achieve sustainability in Thailand. SEP shares the same goals of balanced development as the United Nations Sustainable Development Goals. SEP consists of 2 foundations (knowledge and virtues), 3 principles (moderation, reasonableness, and prudence) and 4 outcomes (economy, society, environment and culture). SEP focuses on developing quality of people, particularly a sufficiency mindset. Therefore, it is important to cultivate this mindset at an early age. The SEP movement in Thai education has started since 2007. Currently, there are 742 Best Practice Sufficiency-based schools and 205 Sufficiency-based Learning Centers that successfully cultivate sufficiency mindset. These schools use action-based learning, questioning, reflection and role modeling to cultivating SEP mindset. By implementing the whole school approach, SEP is used in all school activities and administration. In this case study research, ten Sufficiency-based Learning Centers were studied in 2018. Interview, documentary analysis and observation methods were used. Approximately 13 persons/stakeholders were interviewed in each school. In order to sustain the SEP mindset cultivation in schools amidst changes of school principals and others changes, the findings show that it is important to integrate SEP learning activities with class subjects, thus becoming a part of typical curricular learning. Continuous SEP training and involvement of change agent teachers, all school personnel, change agent students, new school principals and Educational District superintendents are the key success factors for sustainability of the SEP mindset cultivation.