The purpose of this work is to investigate the relationship between the disciplinary diversity of capstone design teams and perceptions of success and engineering design abilities. Capstone design programs are effective environments for students to collaborate with industry sponsors on authentic design problems. They provide students with the opportunity to hone their technical and professional skills, often in teams. Previous work has demonstrated that interdisciplinary teams outperform within-discipline teams on complex open-ended tasks, but struggle to communicate across disciplinary boundaries. They also report lower levels of team cohesion and satisfaction with final outcomes. The results of the mixedmethods study conducted with 58 capstone design teams for this paper indicate that team diversity may be inversely related to students' beliefs in their abilities to construct a prototype. Preliminary qualitative analysis suggests that students tend to divide prototyping tasks based on disciplinary background and struggle to integrate design efforts for complex systems, particularly during later stage design.