The authors developed a novel tool, the CREDIT URE, to define and measure roles performed by undergraduate students working in research placements. Derived from an open-source taxonomy for determining authorship credit, the CREDIT URE defines 14 possible roles, allowing students and their research mentors to rate the degree to which students participate in each role. The tool was administered longitudinally across three cohorts of undergraduate student-mentor pairs involved in a biomedical research training program for students from diverse backgrounds. Students engaged most frequently in roles involving data curation, investigation, and writing. Less frequently, students engaged in roles related to software development, supervision, and funding acquisition. Students' roles changed over time as they gained experience. Agreement between students and mentors about responsibility for roles was high.