The content of sex education in government-funded schools in the USA varies dramatically and reflects its contested nature and goals. Drawing from 50 interviews with sex educators working in the public, government-funded school system in a Midwestern US state, this study explores the processes through which sex educators decide what and how to teach. Working from the theoretical framework of argument sphere theory, and, specifically, socio-scientific controversy, we find that sex educators often resolve the competing arguments they face through processes that we call deliberative conflation and deliberative co-optation. Deliberative conflation involves the use of criteria from one or more argumentative spheres to judge evidence appropriate to a different sphere. Deliberative co-optation involves the use of discourse practices from one sphere to make arguments actually grounded in another. Both of these processes enable the reconciliation of otherwise incommensurate arguments, but they do so in ways that foster unstable and ambiguous curricular decisions. Our findings provide guidance towards improving sex education and its attendant outcomes.