Section — Wouters, Manual of Moral Theology
Scholion II. On Coeducation
Coeducation is to be rejected; this is clear first from the fact that Pius XI, in his encyclical On the Christian Education of Youth, rejects it. "Equally fallacious," says the Supreme Pontiff, "and hostile to Christian training must that method of instructing adolescents be held which is commonly called coeducation." Next, education of this kind, on account of human nature inclined to illicit things and vitiated by the stain of our first parents, is not without danger. It is added that each sex precisely on account of the difference of body and soul must mutually complete itself and coalesce into one thing; hence that very difference must be held and fostered in education and instruction by apt distinction and separation, suitable to ages and conditions. And this must be observed "not only in all schools, through the anxious years of adolescence, on which the plan of almost the whole future life altogether depends, but also in gymnastic games and exercises, in which special care must be taken for the Christian modesty of girls, since it is most unbecoming for them to display themselves and to put themselves before the eyes of all."1
1 Cited encyclical.