Phonsa, K., S. Sroinam, and P. Phongphinyo. “Strategies for Developing the 21st Century Skills of School Principals under Loei Primary Educational Service Area Office”. Asian Journal of Education and Training, vol. 5, no. 1, Mar. 2019, pp. 198-06, doi:10.20448/journal.522.2019.51.198.206.