An early-twentieth-century movement for social purity in England, Canada and the United States aimed to eradicate prostitution, the double standard of sexual morals and their dreaded corollary, the venereal diseases. Social purists suggested that "purity education" for children was the best pedagogical prophylaxis against such medico-moral impurity. Popular purity education guides like the "Self and Sex" Series configured purity education as nature study lessons on reproduction in flora and fauna complemented by a back-to-nature regimen of diet, dress and exercise. Social purists hoped that purity education would induce children to adopt an abstinence agenda promoting heterosexual conventions of chastity before marriage, procreative marital sex and sound parenthood. The Series is used to investigate the ways in which the social purity movement turned to a highly selective vision of the natural order to naturalize the abstinence agenda.