This document summarizes what was learned in a study called SIRF (Strengthening the Implementation of Responsible Fatherhood Programs) that aimed to build evidence on promising practices to improve the enrollment, engagement, and retention of fathers in fatherhood programs. SIRF engaged 10 fatherhood programs in using learning cycles—repeated periods of implementing ideas and reflecting on the results—to assess promising approaches to addressing certain program challenges. The document begins with an overview of the study’s startup, its design, and the learning-cycle processes, then provides a short summary of the promising approaches tested, and concludes with some implications of what the learning cycles found about the tested approaches.