Sex education presents a major dilemma for state‐minority relations, reflecting a conflict between basic rights to education and religious freedom. In this comparative ethnography of informal sex education among ultra‐Orthodox Jews (Haredim) in Israel and England, we frame the critical difference between “age‐appropriate” and “life‐stage” (marriage and childbirth) models of sex education. Conceptualizing these competing approaches as disputes over “knowledge responsibility,” we call for more context‐specific understandings of how educational responsibilities are envisioned in increasingly diverse populations.