Writing activities can function as powerful teaching tools in science education -- but are their benefits realised equitably? The answer may depend in part on how teachers interpret and respond to student writing in light of societal stereotypes that link scientific competence, linguistic competence, and racial, ethnic, or gender identity. In this experiment, high school biology teachers (n = 70) in a U.S. state evaluated and gave feedback on a purported student writing sample. No main effect of student writers' racialised/gendered identity was found; however, non-Hispanic White teachers gave lower ratings when the writing sample was attributed to a Latina female student rather than a non-Hispanic White male student. The reverse pattern was apparent in the ratings of Hispanic teachers and other teachers of colour. All teachers wrote generally similar feedback, but non-Hispanic teachers of colour and White teachers wrote shorter feedback to a Latina student when 'her' score was low, a relationship which did not appear in feedback written to a non-Hispanic White male student. Although most of these disparities did not exhibit statistical significance, many effect sizes were relatively large and may merit further study. Practical implications for equity in science education are discussed.