In laboratory studies, induced stereotype threat shows negative effects on academic performance and learning. Is the relation between stereotype threat and grades robust in naturalistic settings, specifically in introductory STEM courses? We gathered data on two new measures we term race and sex stereotype bias, which were administered four times over the course of introductory chemistry and biology courses for STEM majors (N = 1358). Patterns of growth for all stereotype bias measures showed a discontinuous pattern, with increases during each semester (fall and spring) and decreases between semesters. For all stereotype bias measures, sophomores scored significantly higher than freshmen, and juniors scored in between. For the sex stereotype bias measure, females scored significantly higher than males. There were no race or sex differences on slopes of growth; though groups began at different levels, all grew at the same rate. There was little relation between grades and stereotype bias when analyzed by race; Asian students showed the largest number of significant - albeit small - correlations (3) and Black students the fewest (none). Correlations between grades and sex stereotype bias were significant and negative - but small - only for males. Results support a point made by Steele in 1997 but neglected since then; stereotype threat may affect only a small sub-portion within stereotyped groups. We argue that variables other than stereotype threat might be better targets for research attempting to explain gaps in STEM achievement and retention. (C) 2013 Elsevier Inc. All rights reserved.