Process evaluation was used to explain the success of a randomized, controlled trial of an educational intervention to improve the feeding behaviors of caregivers and the nutritional status of infants in Trujillo, Peru. Health personnel delivered a multicomponent intervention within the environment of usual care at government health centers. We created a model of the expected intervention pathway to successful outcomes. Process data were then collected on health center implementation of the intervention and caregiver reception to it. Using multivariate models, we found that variables of health center implementation, caregiver exposure, and caregiver message recall were all significant determinants in the pathway leading to improved feeding behaviors. These outcomes were consistent with our original intervention model. Further support for our model arose from the differences in caregiver reception between intervention and control centers. Process data allowed us to characterize the pathway through which an effective nutrition intervention operated. This study underscores the importance of including process evaluation, which will lead to the development and implementation of more effective nutrition interventions.