The New Generation Schools (NGS) reform in Cambodia was launched in 2015 with the aim of improving the quality and relevance of education to better prepare Cambodian youth for the twenty-first-century workforce. The reform aims to develop students' cognitive competencies, with a particular focus on STEM, ICT, and critical thinking skills, as well as inter-and intrapersonal competencies. As of 2018, the reform operated in 10 designed "New Generation Schools" across the country which combinedly served over 4,000 students. New Generation Schools are unique in that they operate similar to charter schools in the United States, where school-based administrators and staff have a high degree of autonomy over school operations, resources, curriculum, and instruction. This is coupled with high professional standards that hold schools accountable for improving the quality of teaching and learning in their schools. To support teachers in using their autonomy to deliver innovative, twenty-first century instruction, the reform includes a robust teacher professional development program based on a reflective teaching model. The professional development program employs a variety of modalities, including pre-service training, professional learning communities, career path planning, individual feedback, classroom observations, visits to other schools, and ongoing in-service training. Ultimately, as the reform scales, it aims to create a larger cultural shift in the education system by professionalizing the role of the Cambodian teacher. The NGS reform provides valuable insights for practitioners, researchers, policymakers, and funders looking to enhance teacher capabilities to deliver twenty-first century instruction through a combination of high professional standards and robust professional development.