<p>This study examines whether and under what conditions students make stereotyped judgments about the teaching competencies of female mathematics teachers based on their physical appearance. Drawing on Thompson’s biopsychosociocultural framework, the research adopts a three-phase design involving Mexican engineering students and a participating female teacher. Empirical data were collected through individual interviews, online questionnaires, anonymous institutional evaluations, and a semi-structured interview with the teacher. A qualitative content analysis was conducted to identify evaluations of teaching competencies and appearance-specific reactions. Findings reveal that while most students evaluated the teacher’s pedagogical and mathematical competencies, a subset expressed appearance-based judgments, especially under conditions of anonymity and in the absence of teacher authority. These judgments were sometimes framed in stereotypical terms, suggesting that perceptions of professional competence can be shaped by physical appearance. The teacher’s testimony further illustrates how these evaluations impacted her sense of professional identity, emotional well-being, and instructional practices. This study contributes to mathematics education by foregrounding appearance-based stereotyping as an underexplored form of bias in mathematics education.</p>