Kantatong, W. “The Development of a Model for Volunteer Spirit of The Lower Secondary Level Student in Opportunity Expansion School in Thailand”. Journal of Multidisciplinary in Humanities and Social Sciences, vol. 6, no. 1, Feb. 2023, pp. 234-45, https://so04.tci-thaijo.org/index.php/jmhs1_s/article/view/261984.