I have read some interesting papal quotes recently. . .
Here we have a condemnation of co-education, and so-called 'sexual education' which I agree with him about how distasteful a terminology it is.
"Surely, equally false and harmful to Christian education is that method of instructing youth, which is commonly called "coeducation." Both the sexes have been established by God's wisdom for this purpose, that in the family and in society they may complement each other, and may aptly join in any one thing; for this reason there is a distinction of body and of soul by which they differ from each other, which accordingly must be maintained in education and in instruction, or, rather ought to be fostered by proper distinction and separation, in keeping with age and circumstances. Such precepts in accord with the precepts of Christian prudence are to be observed at the proper time and opportunely not only in all schools, especially through the disturbed years of youth, upon which the manner of living for almost all future life entirely depends, but also in gymnastic games and exercises, in which special care must be taken for the Christian modesty of girls, inasmuch as it is especially unbecoming for them to expose themselves, and to exhibit themselves before the eyes of all."
". . . much more pernicious are those opinions and teachings regarding the following of nature absolutely as a guide. These enter upon a certain phase of human education which is full of difficulties, namely, that which has to do with moral integrity and chastity. For here and there a great many foolishly and dangerously hold and advance the method of education, which is disgustingly called "sexual," since they foolishly feel that they can, by merely natural means, after discarding every religious and pious aid, warn youth against sensuality and excess, by initiating and instructing all of them, without distinction of sex, even publicly, in hazardous doctrines; and what is worse, by exposing them prematurely to the occasions, in order that their minds having become accustomed, as they say, may grow hardened to the dangers of puberty."
You can read more of the above in his Encyclical, "Divini illius magistri"
Pope St. Pius X's quotation in the database, puts it all much more succinctly:
'Obviously the need of this Christian instruction is accentuated by the decline of our times and morals. It is even more demanded by the existence of those public schools, lacking all religion, where everything holy is ridiculed and scorned. There both teachers' lips and students' ears are inclined to godlessness. We are referring to those schools which are unjustly called neutral or lay. In reality, they are nothing more than the stronghold of the powers of darkness.'
Pope Leo XIII, and Bl. Pope Pius IX, amongst others sound the same notes.