The adoption of engineering design-based science teaching requires elementary teachers to modify their current science pedagogy, often resulting in tensions or hard choices they must make in their teaching practice. The purpose of this study is to identify, compare, and characterize the tensions faced by 45 grade 3 and grade 4 elementary teachers over the course of 2 years within the context of a large-scale math-science partnership aimed at improving student learning of science through design and what mitigating strategies they employed to relieve these pressures. Data were gathered using semi-structured interviews prior to and after implementation. Transcripts of these interviews were analyzed using open coding. Findings indicate that within 1 year, teachers' challenges shifted from conceptual and pedagogical in quality to more multifaceted and cultural, reflecting the nature of engineering design and emphasizing teachers' changing roles to facilitate student small group interactions. Mitigating strategies were related to the type of tensions described by teachers, the majority of which became apparent through teachers' repeated enactments of engineering design. Despite facing tensions, teacher participants expressed purposeful intentions to continue using engineering design to teach science. Implications included unearthing engineering design-based science teaching as a reflective teaching approach deeply connected to the nature of engineering that promotes the development of student-centered teaching practices. Ways of connecting these findings with professional development and teacher preparation are discussed.