In South Africa, high pregnancy and infection rates show that many teenagers are having sex, and that they are not adequately protecting themselves against undesired pregnancies and disease. Sex education is usually taught as part of the subject area Life Orientation. In a qualitative study of 25 Life Orientation teachers in the South African Free State Province, we used semi-structured interviews to explore the ways in which these teachers understand gender to be a factor in learners' experiences of sexuality. Our analysis draws upon the conceptual framework of heteronormativity, a key aspect of which is that girls and boys are socialized into different gender roles in ways that propagate the patriarchy, and these are largely viewed as part of the natural order of things. Our data revealed a tendency for teachers to cast boys as largely predatory and girls as victims of sexual predation, either by their peers or by older boys or men. Although these assumptions reflect some of the everyday experiences in South Africa and many other countries, these expectations may be transmitted and reinforced unconsciously in well-meaning educational interventions meant to protect girls.