In K–12 schools, practices of dividing students by biological sex or gender into binary categories limit possibilities for students' identification and representation. Dividing students according to their socially recognized sex or gender reinforces the perceived stability of binary male/female sex and binary masculine/feminine gender categories while also exceptionalizing transgender identities. Students and teachers who challenge such practices engage in critical literacy readings of school spaces and of the mundane ways binary gender and sex are read onto bodies. Critical literacy provides a method through which students and teachers may engage in reflection and critical practice to raise awareness and challenge everyday practices in schools that construct boys and girls as stable, discrete categories. Drawing on three years of ethnographic research in an urban public high school, this article examines the ways teachers and students enact, respond to, and subvert practices that articulate and distinguish categories of boys and girls.