Here is a fascinating finding
We study grading outcomes associated with professors in an elite university in the United States who were identified using voter registration records from the county where the university is located as either Republicans or Democrats. The evidence suggests that student grades are linked to the political orientation of professors: relative to their Democratic colleagues, Republican professors are associated with a less egalitarian distribution of grades and with lower grades awarded to Black students relative to Whites.
Regarding the last result, the authors note:
An obvious question that arises regarding the second finding is whether and to what extent Democratic professors discriminate in favor of Black students or Republican professors discriminate against them. At this stage we only note that in the absence of an appropriate benchmark for comparison, this question cannot be credibly answered.
Thanks to Mark Perry for the pointer.