Design-based learning has been recognized by educational scholars as the key approach to science, technology, engineering, and mathematics (STEM) education at K-12 levels. However, it is unclear whether, and which dimensions of, design thinking mindsets support the conceptual learning of science. This quasi-experimental study aims to explore 37 eighth-grade students' conceptual learning and design-thinking mindsets in the context of design-based learning on pulleys. A conceptual test on pulleys and a Likert scale questionnaire, measuring design-thinking mindsets were administered to the students before and after the design-based learning treatment. In a comparison between two classes of students, using Mann-Whitney U tests in each measurement, some dimensions of design thinking mindsets that facilitate conceptual learning on pulleys were identified. These include: (a) orientation towards learning by making and testing; and (b) mindfulness of the process and impact on other people. Based on these results, recommendations were made for the effective enactment of design-based learning to develop students' scientific understanding.