There is a shortfall of girls and women pursuing STEM disciplines, a deficit that may be partially attributed to subtle forms of bias that are tied to traditional gender role stereotypes. The current study examined these subtle biases in high school teachers and students in two ways: by asking teachers and students to attribute masculine and feminine traits to the typical scientist or humanities professional, and by inquiring about the academic performance assumed of boys and girls. In addition, students were surveyed about their own self-efficacy in math and science courses and gender-balanced teaching initiatives present in the classroom. Results showed that teachers and students exhibited subtle bias by attributing more masculine characteristics to a scientist and feminine characteristics to the humanities. Teachers and students also reported their belief that boys tend to perform better than girls in STEM disciplines. Finally, our results echoed previous literature examining self-efficacy discrepancies for girls in math and science classes, and indicated a lack of gender-balanced teaching initiatives in math and science classes. These results have broad implications for the lack of women in STEM disciplines, and they also reveal a potential means of classroom intervention to help counteract these subtle forms of bias.