A vast research literature documents racial bias in teachers' evaluations of students. Theory suggests bias may be larger on grading scales with vague or overly-general criteria versus scales with clearly-specified criteria, raising the possibility that well-designed grading policies may mitigate bias. This study offers relevant evidence through a randomized web-based experiment with 1,549 teachers. On a vague grade-level evaluation scale, teachers rated a student writing sample lower when it was randomly signaled to have a Black author, versus a White author. However, there was no evidence of racial bias when teachers used a rubric with more clearly-defined evaluation criteria. Contrary to expectation, I found no evidence that the magnitude of grading bias depends on teachers' implicit or explicit racial attitudes. [Funding for this report was provided by a James H. Zumberge Individual Research Award from the University of Southern California.]