Understanding the social influences on positive instructor-student interactions and relationship quality is critical to supporting biomedical workforce diversity and success in Science, Technology, Engineering, Mathematics, and Medicine (STEMM) (National Institutes of Health, 2019; Estrada et al., 2018). This study aimed to experimentally test the impact of a “Creating Birds of a Feather” (CBoaF) intervention (Gehlbach et al., 2016) designed to increase perceptions of instructor-student similarities (psychological similarity) in college biology Course-based Undergraduate Research Experiences (CUREs) and thereby increase Instructor-Student Mentoring Relationship (ISMR) quality. We found that the CBoaF intervention boosted perceptions of psychological similarity among students who initially expressed low levels of perceived similarity. Furthermore, the intervention had a positive indirect effect on student perceptions of ISMR quality through its influence on their perceptions of similarity with their instructor. These findings have implications for designing effective mentoring interventions tailored to enhancing instructor-student relationships.