Background: Teacher educators have begun exploring the most effective ways to prepare preservice teachers (PSTs) to engage elementary students in engineering design. However, this remains challenging as PSTs continue to report a lack of exposure to engineering during their K-12 school experiences. This study investigates the engineering-related knowledge and beliefs of PSTs in their first education course, collaborating in small teams to lead elementary students in engineering design challenges. We explored two different iterations to understand how the structure of the teaching experiences contributed to PST outcomes as a first step in identifying helpful approaches. In spring 2022, PSTs collaborated with undergraduate engineering students to develop and teach a carnival-themed design challenge lesson, while PSTs from fall 2022 collaborated with education classmates to teach a premade engineering lesson focused on designing plastic filters. We used quantitative and qualitative measures to analyze PSTs knowledge of engineering, knowledge of engineering pedagogy, beliefs about the importance of elementary engineering instruction, self-efficacy for teaching engineering, and intention to integrate engineering in their future instruction. Results: Teaching engineering had a positive influence on PSTs' engineering-related knowledge and beliefs. PSTs began to understand engineering as a process and see the ubiquity of engineered products in everyday life. They recognized their teaching role as guiding students through the design process and practices. PSTs noted how elementary students found engineering fun and engaging and were able to develop successful solutions with minimal assistance and even persevered through failure. These observations contributed to the development of their engineering-pedagogical knowledge and helped cultivate positive engineering-related beliefs. Following their teaching experiences, most PSTs gained self-efficacy for teaching engineering, believed engineering should be taught in elementary schools, and had an intention to integrate engineering into their future instruction. Conclusions: Our findings suggest teaching engineering to elementary students is an effective approach to enhancing beginning PSTs' engineering-related knowledge and beliefs. Recommendations are made for structuring teaching opportunities early in preparation programs, including: teaching elementary students, practicing teaching, and engaging as students in meaningful design challenges. Questions remain regarding how best to structure teaching experiences for early PSTs, such as ideal team composition and placement in elementary teacher education programs.