In 2016, a clinical skills building mentorship approach was implemented in two provinces of northern Lao. The aim was to build the skills of maternal and newborn health providers to provide quality care at the time of birth. After 2 years of implementation, there was a need to evaluate the efficacy of the program. From observation, there were differences in program outcomes in the two provinces. Realist evaluation is a relatively new research methodology, but is well suited to evaluating programs in complex systems. Unlike other evaluation methods, the theory-driven approach takes a multidimensional view and considers not just “does a program work?” but explores how it works, where, and why. Three core components comprise realist evaluation, namely, context, mechanisms, and outcome. Results from realist evaluation are then used to re-evaluate and re-conceptualize the original program theory to ensure it is consistent with the reality of on the ground implementation. This case study will describe how a realist approach was used to evaluate a clinical skills building mentoring program and will reflect on the utility of using this research methodology.