The new standards for K-12 science education in the United States call for science teachers to integrate engineering concepts and practices within their science teaching in order to improve student learning. To accomplish this, teachers need appropriate instructional materials as well as the knowledge and skills to effectively use them. This mixed methods study examined participants' perceptions of a STEM education partnership project in which university faculty members and elementary school teachers collaborated to develop and implement engineering design-based materials in elementary science education. Quantitative survey results suggested that both university faculty members and participating school teachers demonstrated elements of collaboration characteristic of an effective community of practice, and qualitative data from open-ended survey responses and interviews identified the factors that participants viewed as important. Results suggest that collaborations among community of practice participants are important to the success of school-based STEM education reform initiatives like the one described here.