Supplemental instruction (SI) is a small-group, peer-mentored programme which is compatible with the learning preferences of American Indian students. We tested the hypothesis that SI is a compensatory strategy that reduces the differences in the grades earned in introduction to psychology by Euro-American and American Indian students. The sample consisted of 129 American Indian students and 4588 Euro-American students enrolled in introduction to psychology at a US university. As hypothesised, a multi-level model yielded a significant (p < 0.01) interaction between SI and ethnicity on course grade. Whereas for non-SI users, the gap between Euro-American and American Indian students was 0.71 grade points, for SI users, it was only 0.15 grade points. Strategies should be devised for increasing SI visits by students enrolled in introduction to psychology, particularly those who belong to American Indian tribes.