Research has shown that both learners and teachers struggle to understand and teach geometric transformations meaningfully. This mixed-methods case study examined the efficacy of the Student Teams Achievement Division (STAD) cooperative learning model in fostering learners’ conceptual understanding of geometric transformations. This study involved 28 Grade 12 learners from one intact class. In addition to pre- and post-intervention tests, which measured learners’ conceptual understanding of geometric transformations, participants completed a feedback questionnaire at the end of the intervention. The results show that the STAD model significantly improved learners’ grasp of geometric transformations, as demonstrated by higher test scores in the post-test. Participants also highlighted the importance of well-crafted questions during group discussions and oral quizzes, teacher explanations during whole-class presentations, and the motivational impact of criteria for selecting and awarding top-performing groups. Based on Shapiro’s intervention evaluation criteria, the STAD model was found to be effective, with high levels of acceptability, integrity, and social validity. While this study confirms the STAD model’s effectiveness in enhancing conceptual understanding and social learning, it also emphasizes the importance of considering contextual factors, such as group dynamics and classroom resource availability, when implementing this cooperative learning model. Teachers are encouraged to tailor this learning strategy to their specific classroom environments and learners’ needs.