jobs. Evaluation of the workshop relied on registration data, pre-/post-surveys, and performance data from the learning management system. 440 completed at least one assignment, 224 completed at least 80% of the assignments, and 191 completed all 35 assignments, significantly higher than most comparable large-scale, open-access courses. Participants invested ~6 hours per week and averaged a score of 88% on assignments. We identified >60% normalized gain in scientific computing skills. There is evidence the inclusive design of the workshop was able to attract and retain a diverse population. However, some additional investigation is needed to ensure benefits were evenly experienced. Regardless of the degree of completion, participants perceived the workshop quite positively: on average 96% described it as high to very high quality, 83% satisfied to very satisfied with their experience, and 70% very likely to recommend to peers. We identify future directions for running a second iteration of the workshop, including strategies to continue broadening participation and improving retention. 1. Introduction 1.1. Setting and Motivation. Undergraduate research opportunities, like the Research Experience for Undergraduates (REU) program run by the Incorporated Research Institutions for Seismology (IRIS), have become critical stepping stones in the career development of future seismologists, like most other geoscience and STEM fields (Mogk, 1993;Lopatto, 2007). Since 1998, IRIS's summer internship program has facilitated opportunities for 220 undergraduate students to conduct seismological research and produce research products worthy of presentation and recognition at large professional conferences. Alumni of this program have described the program as highly influential on their educational career trajectories (Hubenthal, 2018). This aligns well with the body of literature on undergraduate research opportunities (UROs), which suggests that participating in it can improve retention of students in STEM majors and increase students' interest in pursuing STEM graduate programs, contribute to students' understanding of disciplinary knowledge and practices, and integrate students into the scientific culture (NASEM, 2017). More recent comparative work has shown that when controlling for a number of factors, REU participants are more likely to pursue a PhD program and produce valuable research