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Teachers’ Biases Show up in Report Cards

A study involving over 14,000 ninth graders in Germany has uncovered significant grading biases associated with students’ gender, body size, ethnicity and parental socioeconomic status. The study highlights the need for further research into the causes and solutions to these pervasive biases in education.
Certain students are disadvantaged in grading because of their gender, height, ethnicity and the socio-economic status of their parents. (Image:
Certain students are disadvantaged in grading because of their gender, height, ethnicity and the socio-economic status of their parents. (Image:

Secondary school grades can open or close doors to careers later in life. To investigate whether students suffer from bias in their school grades, Richard Nennstiel and Sandra Gilgen of the University of Bern and the University of Zurich used data from the National Educational Panel Study in Germany, a study that has followed seven cohorts of German students since 2008.

The researchers focused on a nationally representative sample of 14,090 students who were in the ninth grade in 2010. Nennstiel and Gilgen compared grades given by teachers with scores on standardized competence tests to see whether some students had an advantage over others. The researchers looked at the effects of gender, body mass index (BMI), parental socioeconomic status and ethnic background.

Slim girls from affluent, non-immigrant families get the best grades

The study confirmed that students are exposed to a significant grading bias based on their gender, body size, ethnicity and parental socioeconomic status. These negative biases are compounded, meaning that students with multiple intersectional identities receive significantly lower grades than their peers, regardless of their actual ability.

Gender bias in teacher-assigned grades was evident in all subjects except chemistry. Girls had an advantage in German, mathematics and biology, while boys had an advantage in physics. Higher BMI was associated with significantly lower grades in every subject, while students from wealthier families generally had higher grades. Minority students received lower grades in all subjects except biology.

These disadvantages were cumulative, meaning that regardless of actual ability and aptitude, a boy with a high BMI from a lower socioeconomic and minority background received lower grades on average than a German-born girl from a higher socioeconomic background with a low BMI.

Widespread biases among secondary school teachers

While these findings do not determine the exact mechanisms behind this discrepancy, they suggest that grading bias is widespread among teachers in Germany. The researchers recommend that further studies focus on why students receive biased grades, and how such biases could be addressed in the classroom.

The authors add: “Even after controlling for three different measures of ability and school track attended, we find widespread additive intersectional effects of gender, social and ethnic origin, and body weight on grading.”



Richard Nennstiel and Sandra Gilgen. Does chubby Can get lower grades than skinny Sophie? Using an intersectional approach to uncover grading bias in German secondary schools. PLOS ONE. 3 July 2024. DOI: 10.1371/journal.pone.0305703.

Weiterführende Informationen


Dr. Sandra Gilgen
URPP Human Reproduction Reloaded | H2R
Empirical and Normative Knowledge and Data Centre
Department of Sociology
University of Zurich
+41 44 635 23 44