Palatip, P., and W. Keeratichamroen. “A Study of Learning Achievement on Law and Politics for Life Learning Unit and Critical Thinking Ability of Grade 8 Students Using Problem Based Learning with Concept Mapping”. Ratchaphruek Journal, vol. 18, no. 2, Aug. 2020, pp. 74-81, https://so05.tci-thaijo.org/index.php/Ratchaphruekjournal/article/view/220236.