Professional advancement often depends on subjective performance reviews, especially in developing countries where objective data on performance may not be available. But subjective reviews may be susceptible to personal biases based on characteristics like gender. To better understand this in the education sector in Ghana, researchers compared both principals’ reviews and teacher self-assessments of effectiveness to an objective measure:  increases in student test scores. Female teachers were objectively more effective based on increases in student test scores. However, principals were 11 percentage points less likely to rate a female teacher as effective compared to a male teacher. These findings contribute to the evidence on gender biases in subjective assessments and related barriers faced by women in labor markets in developing countries.