Sawaengmongkon, C. “A Comparison of Standard Thai Achievement of Ethnic Karen First Grade Students in Monolingual Thai, Informal Bilingual Thai-Karen, and Mother Tongue-based Multilingual Education Classrooms”. Journal of Education Studies, Chulalongkorn University, vol. 42, Dec. 2014, pp. 33-47, https://so02.tci-thaijo.org/index.php/EDUCU/article/view/26458.