Conflation of sex and gender is implicated in the development of essentialist thinking, which has been linked to the justification of systems of prejudice in modern society. This exploratory study presents findings from a person randomized control trial conducted with 460 students in 8th-10th grade that investigated the extent to which students conflate sex and gender in their writing about genetics. Students were randomly assigned to one of three short readings that either (1) explained the genetics of sex in plants; (2) explained the genetics of sex in humans; or (3) refuted neuro-genetic essentialism, offering instead a social explanation for why women receive fewer PhDs in science, technology, mathematics, and engineering than men. While previous findings from the authors suggest links between the condition students were assigned to and psychological indicators related to essentialist thinking, no work was done to investigate how students' use of language might implicate cognitive conflation as a possible factor in understanding these results. In this study, student responses to a constructed response writing task given after the reading were analyzed to investigate the use of sex and gender language. Students in all three conditions used both sex and gender language. However, students in the refutational text condition tended to use sex and gender language deliberately in order to explain PhD attainment, while students in the traditional genetics conditions used the terms interchangeably, suggesting subconscious conflation. Students in the genetics of human sex condition were more likely to manifest this conflation than students in the genetics of plant sex condition. Implications for instruction are discussed.