Educators and researchers often think of program design and program evaluation as separate endeavors, even intentionally creating a firewall between them. But what if designers and evaluators worked together, combining their insights to strengthen both the program and the study of it? In the work of evaluating a statewide professional learning program in Tennessee, the authors have found this approach benefits everyone involved. In this article, the authors share strategies for a collaborative approach to evaluation, show how this approach is improving our ability to develop meaningful data collection tools, and conclude with three specific lessons for collaborative design. Because this initiative serves teachers who are not content-area experts in computer science, we believe our approach is applicable to evaluating professional learning in any content area.