Field courses have been identified as powerful tools for student success in science, but the potential for field courses to address demographic disparities in science is little-explored. We examined (a) effects of an introductory field course on students’ perception of their scientific competencies, and (b) how the field course shaped student experiences and built their sense of community, confidence and belonging in science. We focused on a non-majors EEB course, Introduction to Field Research, at the University of California-Santa Cruz (UCSC), a large Hispanic-Serving Institution. Our mixed-methods approach included pre- and post- course surveys with field course students and a control group; interviews, focus groups and prompted student journal entries with a subset of field course students; and participant-observation in a fall 2019 offering of the course. We found that field course participation in general at UCSC was associated with higher science self-efficacy gains, GPA and graduation rates. Students who took Introduction to Field Research experienced especially large science self-efficacy gains if they started with low self-assessed science competencies. As a result, the course closed science confidence gaps between students from marginalized and well-represented groups. Themes of growth in peer community, relationships with mentors, confidence living and working outdoors, team-based science skills and experience, and a sense of contributing to knowledge and discovery interacted throughout the course – especially from the initial overnight field trip to the final one – to yield these confidence gains and cement interest in science careers or incorporation of science into other disciplines. We discuss how field course design and implementation can enhance inclusion, reduce demographic gaps in science, and inspire students to pursue collective discovery and excellence in their academic careers.