This study examines the influence of pupil and teacher characteristics on the diagnostic competence of teachers in the context of educational disadvantage in Germany. Congruent with the stereotype threat theory, it is expected that female gender and migration background will have a detrimental effect on the teacher assessment and that these persons will therefore be wrongly negatively judged. On the teacher side, it is investigated how gender and work experience influence the diagnostic competence. A total of six 11th grade classes (N = 156) were assessed by 18 teachers. The results show that, contrary to the expectations and independent of teacher variables, female pupils are more correctly and better assessed than male pupils. However, only experienced teachers were able to assess persons with a migration background without being influenced by them. There is thus an increased need to sensitize teachers to the impartial assessment of people with a migration background.