Background: Course-based research experiences (CBREs) are highly valued for science learning and research. Most are discipline-centered, but there is a great deal of interest in developing them to promote interdisciplinarity. Yet, we have much to learn about how CBREs work, and even more to learn about how disciplinary diversity operates as an element of design to promote learning and research. Method: This mixed methods case study triangulates data on student experience, research networks, research artifacts and fieldnotes from participant observation to understand how disciplinary diversity factors into productive engagement for learning and research in an interdisciplinary course-based research experience (I-CBRE). Findings: A common boundary object (scientific paper) mediated developmental interactions among individuals both within and beyond the course. The boundary object also facilitated the productive engagement of students as instrumental actors in broader interdisciplinary research networks. Contribution: This study shows how an "object tracing" approach can be used to examine productivity in disciplinarily diverse scientific contexts, and reveals some of the distinctly syncretic moves that participants deploy to make progress as learners and researchers. Extending work by Engel and Conant, the study emphasizes the importance of designing for "productive syncretic engagement" in research experiences characterized disciplinary diversity.