Consistent with an international trend toward education for sustainable development, this chapter describes the rise of the sufficiency-based school movement in Thailand. This movement promotes sustainability education by developing sufficiency thinking in school students from primary school onwards. It does this by embedding sufficiency thinking principles in the curriculum in age-appropriate ways, and encouraging school administrations to role-model the principles. A whole-of-school approach has been adopted to apply sufficiency thinking to all school activities, from management and student activities to community partnerships. Schools can become certified 'sufficiency-based' schools. By October 2015, about 46 per cent of Thai schools has been certified as sufficiency-based. Accredited Sufficiency Educational Learning Centres (SELCs) mentor applicant schools to help them become sufficiency-based. So far 68 schools have qualified as SELCs. Sufficiency principles are integrated directly into relevant lessons and indirectly, as decision-making principles, into other subjects. This chapter describes the processes of establishing, assessing and encouraging sufficiency schools. It reports on a qualitative study of nine SELCs, and compares the findings with international research. Challenges for the future of the sufficiency movement in Thai schools are also discussed.