U-thaisaeng P. The Development of an Instructional Model to Promote the Ability to Solve Mathematical Problems for for Nineth Grade Students. J Roi Et [internet]. 2020 Aug. 20 [cited 2025 Dec. 10];14(2):63-75. available from: https://so03.tci-thaijo.org/index.php/reru/article/view/207883