STEM education is gaining popularity in primary and high school curricula worldwide, emphasizing effective instructional methods. This article discusses a case study using the Technology Design Process (TDP) to create teaching materials to introduce variables and functions in a mathematical context at the elementary level. The TDP's iterative stages were used in the development, and data was collected from different sources: pre- and post-questionnaires, as well as a working document dealing with pupils’ understanding based on designing, making, testing, and simulating. Nineteen students from a fourth-grade classroom (9–10 years old) participated in the study. The results indicate that STEM activities enhance classroom engagement and math learning while fostering problem-solving skills in a transdisciplinary context. This research encourages elementary teachers to incorporate more STEM activities and emphasizes the importance of the design process for critical thinking and practical skills. It also suggests that technology teachers include these design process steps in their teaching to develop engineering design skills and spark student interest in STEM subjects.