This paper aims to provide insights into recent events concerning school sex education in Japan. A campaign of criticism against school sex education emerged in 2002 at both national and regional levels, and included a court case in Tokyo. Despite leaving a depressing atmosphere regarding sex education teaching practices, this campaign also functioned to generate new research, which not only brought together the first nationwide data on school sex education, but also revealed hitherto unknown facts. The evidence uncovered indicated that the campaign against school sex education was not supported by wider society, and restrained routine reactions by the central government served as a buffer against criticism to suspend it.