In the recent past the coffee production sector witnessed a rapid expansion of certification programs promoting voluntary sustainability standards, one of which is UTZ Certified. In this article we assess the impact that this program has on participating smallholder farmers by reviewing the results of an agent-based simulation for modeling rural producer organizations. We present the developed empirical simulation model by sharing the common protocol, which documents the structure the applied simulation tool and its parameterization for the group of coffee farmers, and reporting the results of model validation. The main strength of this assessment is that it considers certification-related costs of the farmers, which are ignored in the analyses available so far. The obtained simulation results constitute quantitative evidence of UTZ certification being able to create considerable positive impacts on the participating farmers. The results outline the importance of external financing and supportive measures complementing certification in groups.