In this article we investigate whether engagement through collaborative project-based learning (PBL) can boost trusting behavior. We experimentally tested if working in teams on a PBL project during a 15-week semester leads to developing a higher level of trust as compared to working on class assignments individually. We found that trusting behavior in the trust game, on average, is stable and does not change significantly over time. We also found heterogeneity of the behavioral response with the change in trusting behavior depending on starting levels. Those starting with higher trust levels stay the course, while those with lower initial trust levels tend to build up trust regardless of class format. But it is only for learners beginning the term with moderate trust levels that PBL instruction boosts trusting behavior compared to non-PBL classes. These results underscore the complexity of trusting behavior and the importance of accounting for heterogeneity when designing interventions. Understanding how learning affects trust may be useful for designing teaching approaches that bolster prosocial behavior and cultivate social capital for less divided societies.