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 our work evaluating a statewide professional learning program in Tennessee, we have found this approach benefits everyone involved. Since 2022, we’ve undertaken an ambitious task of evaluating the Reach Them All computer science initiative’s professional learning for school- and district-level educators across Tennessee (see sidebar on p. 49). We have engaged in a collaborative evaluation design process that started at the beginning of the initiative to explore how the professional learning program works. We made strategic evaluation decisions based on the program