Latest standards-based reform documents from mathematics and science education organizations and communities bring forward one important issue--higher-order thinking skills, namely reasoning. In this article, we share our experiences and our approach to developing an integrated course for mathematics and science prospective teachers centered on fostering reasoning with the use of technology. This study took place in an integrated mathematics and science methods course. The prospective teachers were career changers with STEM (science, technology, engineering, and mathematics) backgrounds. A sociocultural theoretical approach framed this study, wherein learning is evident in the constructed and enacted plans to engage STEM students in reasoning. The analysis of prospective teachers' reflections and integrated lesson plans suggested that the structure of the course scaffold with minilesson study helped prospective teachers extend their view of reasoning and consider reasoning when planning lessons in the future.