Interprofessional education (IPE) has grown in popularity in recent years, but much work remains to be done regarding its evaluation and longitudinal impact, as well as in codifying the attributes of IPE that prepare learners for "collaboration-ready" practice. The present study sought to assess collaboration skill retention or change among graduating seniors who completed an introductory IPE course in 2017, comparing present collaboration skill levels to past levels before and directly after the introductory IPE course using the Self-Assessed Collaboration Skills (SACS) instrument. Additionally, further validation of a collaboration skills instrument was conducted, and qualitative data were gathered to identify collaboration-relevant curricular design elements and generate feedback for continuous program improvement. A final sample of 106 respondents from a variety of professions provided quantitative data, while 91 provided qualitative data. Results suggested that participants retained collaboration skills over the course of their undergraduate education (i.e., 2020 levels as compared to pre-IPE levels in 2017), that IPE evaluation instrumentation requires more cross-contextual and cross-institutional validation, and that students recognize the value in intentional IPE course sequencing for clinical practice. The findings from this study contribute to the further enhancement of IPE outcomes assessment and the design of IPE experiences for fostering collaboration skills among health professional students.