This paper describes the design of a moral education lesson in accordance with a competency-based approach to teaching critical thinking for primary students. Sympathy is selected as a target moral value and used as a theme to teach critical thinking for students. By using literature on competency-based education and critical thinking as a theoretical framework and applying a design-based research approach, this study improves our understanding of how to design a model competency-based lesson and provides a specific exemplary lesson for increasing critical thinking competency in the moral education of primary students. The study suggests a program for teacher professional development using a competency-based approach to train teachers for effective implementation of the designed lesson.