This study aimed to evaluate the effectiveness of a design thinking teaching and learning model on students' design thinking skills in science class. The study utilised two projects, 'Making a Simple Solar Water Heater' and 'Drawing a 3D Topographic Map of Zhejiang Province,' based on the 5th-grade science curriculum in China, and involved 45 Grade-5 students from a primary school. The quasi-experimental repeated measure method was used to evaluate the students' improvement in design thinking skills, with task-based pre-, mid-, and post-tests. Employing quantitative data analysis, the results showed significant improvement in students' overall performance, with more pronounced improvement between the pre-test and post-test than between the pre-test and mid-test. The analysis of the seven design indexes of students' design work demonstrated significant improvement in five indicators, except for 'material' and 'shape.' The study highlights the importance of incorporating design thinking into elementary school curricula to equip students with the necessary competencies for success in the twenty-first-century workforce.