Incorporating technology in classrooms to promote student learning is an ongoing instructional challenge. Teacher professional development (PD) is a central component of teacher education to support student use of technology and can improve student learning, but PD has had mixed results. In this study, researchers investigated a PD program designed to prepare a cohort of middle school social studies teachers to teach with an online resource, the Smithsonian Learning Lab. They examined how an iterative, design-based approach used teacher feedback to develop learning opportunities in the PD. Using the technological, pedagogical, and content knowledge framework (TPACK), they found that through four iterations of 1-day PD workshops, PDs afforded teachers increasingly individualized and meaningful opportunities to learn. Teacher feedback emerged as a central component in the changes and development of the PD series. Through the course of the PD, teacher knowledge increased across five of seven TPACK domains.