Social service programs are often looking for ways to assess and improve program design and implementation, and are increasingly using rapid learning methods to do so. In rapid learning cycles, programs try a new approach, see how well it works, make modifications to strengthen it, and then try it again. This brief illustrates how 10 fatherhood programs used learning cycles to evaluate one of three promising approaches to engaging men in their services, and the ways they used data in the learning cycle process to make decisions about the design and implementation of the approaches. Even outside of the learning cycle framework, programs may benefit from using data and the observations and reflections of participants and staff members to guide the implementation of program elements, as is illustrated in this piece.