This qualitative study examines the influence of a 3-year professional development project for middle school mathematics, science, and special education teachers focused on integrating science, mathematics, and engineering in classroom instruction on participants' understandings of productive struggle in learning. Multi-disciplinary teams of teachers engaged as learners to use engineering design as a framework for integrating significant mathematics and science content supported by effective teaching practices. In this paper, we describe how the components of our professional development design supported teacher-participants to make sense of productive struggle in learning. In particular, participants noted that being able to experience design-based activities as learners and working through solutions with their colleagues supported their understanding of what it means to productively struggle, resulting in their growth as individuals and as teachers. The significance in this work lies in understanding how to effectively support teachers to buy-in to the meaning and value of productive struggle and how engaging in integrated science, technology, engineering, and mathematics (STEM), design-based professional learning experiences facilitated that effort.