This research investigated different forms of sex bias in teacher expectations relative to gymnastics performance. First, a laboratory experiment including 163 physical education teachers confirmed that stereotypes favorable to boys may influence teacher expectations in gymnastics. Next, a naturalistic study involving 15 teachers and 422 students showed that teachers expected no sex differences, even though girls performed better than boys. However, this sex bias was a result of reliance on nondiagnostic student personal characteristics favorable to boys, rather than on a stereotype per se. These results suggest that egalitarian beliefs may mask a bias in favor of a social group when group differences actually exist, and that sex-biased teacher expectations do not inevitably involve an influence of sex stereotypes.