Building working models for evaluation and learning is important to assess the long-term impact of a project. Models can range from a conceptual framework to more sophisticated computer-aided simulations. In some areas where the data is sparse to begin with, how does one build such models from scratch? What methods can be applied to a field of study, such as electronic payments, at the leading edge of development practice? How does one ensure the continued validity of such models over time and harness its predictive power?The presentation dissects these questions within the context of a challenging field of study (electronic payments for financial inclusion) in an emerging economy (the Philippines) that have highly demanding partners (USAID, the Philippine central bank, and dominant payments industry players). It discusses not just the technical aspects of evaluating a project with national impact, but also how external regulatory and programmatic changes influence the monitoring and evaluation function whilst building the evaluation model for e-payments.