In 1999 Thailand passed an ambitious national educational law that paved the way for major reforms in teaching, learning and school management. Despite the ambitious vision of reform embedded in this law, recent studies suggest that implementation progress has been slow, uneven, and lacking deep penetration onto classrooms. Carried out ten years after the launch of the reform law, the current research sought to expand on these earlier studies by examining the capacity of Thailand's principals to lead reforms in teaching and learning. The study developed a national profile of principal instructional leadership using a Thai Form of the Principal Instructional Management Rating Scale (). The overall profile of 1195 primary and secondary school principals suggested a moderate level of engagement in two dimensions (Creating a School Mission and Developing a Positive School Learning Climate) and a lower level of activity on the dimension, Managing the Instructional Program. The results provide preliminary evidence which suggests that a more systematic human resource strategy is needed in order to ensure that Thailand's key school leaders have the knowledge, skills and motivation needed to support changes in teaching and learning envisioned in the nation's education reforms.