First-generation (FG) college students (i.e., those for whom neither parent/guardian obtained a bachelor's degree) experience more barriers in college, compared with continuing-generation students. These barriers are compounded by subtle messages from instructors that convey the idea that natural talent is necessary for success in scientific fields. In contrast, growth mindset messages communicate that ability can improve with effort, help-seeking, and using productive study strategies. In a large enrollment introductory biology course, students were randomly assigned to receive email messages from their instructor after the first two exams containing either a growth mindset or control message. The intervention improved grades in the course for everyone, on average, compared with control messages, and were especially beneficial for FG students. This increase in performance was partially mediated by increased activity accessing course materials on the course website. This study provides preliminary evidence that instructors communicating growth mindset messages can support FG students' performance.