Transfer students typically navigate nontraditional educational pathways in higher education, which often confer institutional barriers to entering science, technology, engineering, and mathematics (STEM) at the university level. The transfer pathway disproportionately consists of underrepresented minority groups, who encounter difficulties in STEM due to intersections of marginalizing experiences across race, class, gender, sexuality, and other identities, given STEM’s historic nature of being built upon white, middle class, masculine, and heteronormative values. Despite their high representation in undergraduate populations and unique identities as university students, transfer students continue to be an understudied population. We interviewed 29 transfer students pursuing STEM degrees who described memorable moments that positively or negatively influenced different dimensions of their STEM identities and identified patterns and variations among their experiences. Our findings highlight three major findings. First, the achievement of good grades emerged as a prominent identity-shaping experience, but students did not report feeling acknowledged or becoming more interested in STEM as a result. Furthermore, students who experience analogous events can interpret them both positively and negatively. Finally, students valued acknowledgment from individuals outside of STEM, such as friends or family, differently than acknowledgment from those in STEM, such as professors or peers. Overall, our findings can be informative to policy makers, faculty, staff, and educational institutions on how to best support transfer students in forming strong STEM identities.