U.S. national data show that American Indians earn lower math and science scores than other ethnic/racial groups. In the current study, a brief, self-affirmation intervention was aimed at increasing science motivational beliefs in American Indian middle school students (n = 212, M[subscript age] = 12.7 years). Students, each read a biography of a successful scientist who was matched to them on both ethnicity and gender; ethnicity but not gender; gender but not ethnicity; or no match. Students then wrote a short essay describing traits they shared with the scientist. Pre- and post-intervention science self-efficacy, individual interest, and goal orientations were measured to assess intervention efficacy immediately following the intervention and one week later. Results revealed no benefits of the intervention in increasing motivational beliefs for students in any experimental condition. We discuss the fragile fidelity of self-affirmation interventions and conditions that might be necessary for intervention success.