While online learning environments are increasingly common, relatively little is known about issues of equity in these settings. We test for the presence of race and gender biases among postsecondary students and instructors in online classes by measuring student and instructor responses to discussion comments we posted in the discussion forums of 124 different online courses. Each comment was randomly assigned a student name connoting a specific race and gender. We find that instructors are 94% more likely to respond to forum posts by White male students. In contrast, we do not find general evidence of biases in student responses. However, we do find that comments placed by White females are more likely to receive a response from White female peers. We discuss the implications of our findings for our understanding of social identity dynamics in classrooms and the design of equitable online learning environments.