What is the role of frontline project leadership in organizational learning in incremental business process improvement (iBPI)? Current literature is sparse on the topic of contributions to organizational learning made by frontline employees leading iBPI projects. To bridge this gap, we use an embedded longitudinal multiple case to study the process of leadership of four frontline iBPI projects. The 4I model (intuiting, interpreting, integrating, and institutionalizing) of organizational learning serves as a theoretical lens to study how the insights originating from frontline employees unfold through group-level integration and organization-level institutionalization. Mapping the flow of key project events to the relevant social and psychological processes of the 4I model, we identify how organizational learning unfolds within and through the three levels of the model. The granularity of the 4I model creates a valuable foundation for informing the role of frontline project leadership in iBPI programs and the capacity to leverage insights originating from frontline employees into organizational learning. Practitioners and engaged scholars will find this level of granularity helpful for program design, evaluation, and learning interventions.