This study investigates the importance of gender and ethnic interactions among teachers and students for school performance in Swedish, English and Mathematics. School leaving certificates assigned by the teacher is compared with results on comprehensive national tests. The analysis is based on data on grade 9 students (age 16) from Sweden. I find that a student is likely to obtain better test scores in Mathematics, when the share of teachers of the same gender as the student increases. Correspondingly, ethnic minority students, on average, obtain better test scores in Mathematics, when the share of ethnic minority teachers increases. The positive same-gender effect on test scores is counteracted by a negative assessment effect. That is, conditional on test scores, same-gender teachers are less generous than opposite-gender teachers when assessing students’ performance. In Swedish and English no statistically significant effects are found.