Research suggests that, to narrow the gender gap in engineering, we should focus on helping young girls identify with engineering both because gendered attitudes emerge around kindergarten and because identity is more predictive than performance on persistence in the field. This qualitative study sought to understand the impact of collaborative engineering design on the development of engineering identities in elementary-school students and compared the findings across gender. We focused on three tiers of collaboration embedded into the engineering design process: peer groups, role models, and shared goals. More specifically, the elementary students worked in small teams and partnered with undergraduate engineers to help design and build dancing robots that come together for a coordinated dance performance. We used ethnographic methods, including pre- and post-program student interviews, video-recorded program sessions, and documentation of student work, to investigate elementary students' engineering identities. Three themes emerged from our analysis. First, working with peers encouraged students who were initially uninterested in engineering, the majority of whom were girls, to join the program and helped them to engage in the activities. Second, partnering with engineer role models contributed to the elementary students' developing identities as engineers: The girls were most influenced by the personal bonds they formed, while the boys were most influenced by the technical skills they learned. Third, all girls and most boys preferred the idea of working toward a shared goal over competitive projects that, as described by the students, can cause bad feelings and hurt friendships. Our work supports and extends elementary engineering literature by considering the role of multiple tiers of collaboration in identity development in girls and boys. Our results suggest that engineering design programs that foster collaboration can help more students, especially more girls, engage in and identify with engineering, thereby contributing to the narrowing of the gender gap.