Аннотация:Significance The scarcity of women in the American science and engineering workforce is a well-recognized problem. However, field-tested interventions outside artificial laboratory settings are few. We provide evidence from a multiyear field experiment demonstrating that women in engineering who were assigned a female (but not male) peer mentor experienced more belonging, motivation, and confidence in engineering, better retention in engineering majors, and greater engineering career aspirations. Female mentors promoted aspirations to pursue engineering careers by protecting women’s belonging and confidence. Greater belonging and confidence were also associated with more engineering retention. Notably, grades were not associated with year 1 retention. The benefits of mentoring endured beyond the intervention, for 2 y of college, the time of greatest attrition from science, technology, engineering, and mathematics (STEM) majors.