This article provides a meta-analysis of experimental research findings on the existence of bias in subjective grading of student work such as essay writing. Twenty-three analyses, from 20 studies, with a total of 1935 graders, met the inclusion criteria for the meta-analysis. All studies involved graders being exposed to a specific type of information about a student other than the student's performance on a task. The hypothesized biasing characteristics included different race/ethnic backgrounds, education-related deficiencies, physical unattractiveness and poor quality of prior performance. The statistically significant overall between-groups effect size was g = 0.36. Moderator analyses showed no significant difference in effect size related to whether the work graded was from a primary school student or a university student. No one type of biasing characteristic showed a significantly higher effect size than other types. The results suggest that bias can occur in subjective grading when graders are aware of irrelevant information about the students.