This paper aimed to enhance primary school students’ critical thinking by implementing an interdisciplinary STEM approach using the inquiry method in science learning of energy and its changing topic. This innovative learning is designed to engage students in constructivism through project-making. This study involved twenty-five-six-grade primary school students at a public primary school in Java Province, Indonesia. The qualitative method was employed to explore and understand students’ experiences during learning in developing five aspects of critical thinking skills SCIT, including identifying questions at issues, conceptual understanding, ideas connection, assumptions, and inferences. The researchers collected the data through classroom observation, reflective journals, interviews, and a concept test. In this study, students are engaged in five learning stages: ask, investigate, create, discuss, and reflect. The findings obtained by the researchers reflected that students were actively involved in all phases of learning. They feel they are challenged to learn through a simple electrical circuit and a simple flood detector project. The analysis showed that students were experiencing the enhancement of critical thinking skills through information exploration and project discussion to engage them in identifying questions at issues raised in the learning. Besides, facilitating students to integrate their thought into real-life and project-making leads them to improve their conceptual understanding. In addition, interdisciplinary learning encouraged them to connect ideas and make assumptions and inferences by considering multiple perspectives on developing a project.