Promtrud, A. and Vibulrangson, S. 2023. Developing Learning Activities Using an Open Approach Together with Assessment for Learning to Promote Mathematical Competencies of Ninth Grade Students . Journal of Education Studies, Chulalongkorn University. 51, 4 (Dec. 2023), EDUCU5104010. DOI:https://doi.org/10.14456/educu.2023.37.