80 For the mere fact that a school gives some religious instruction (often extremely stinted), does not bring it into accord with the rights of the Church and of the Christian family, or make it a fit place for Catholic students. To be this, it is necessary that all the teaching and the whole organization of the school, and its teachers, syllabus and text-books in every branch, be regulated by the Christian spirit, under the direction and maternal supervision of the Church; so that Religion may be in very truth the foundation and crown of the youth's entire training; and this in every grade of school, not only the elementary, but the intermediate and the higher institutions of learning as well. To use the words of Leo XIII: It is necessary not only that religious instruction be given to the young at certain fixed times, but also that every other subject taught, be permeated with Christian piety. If this is wanting, if this sacred atmosphere does not pervade and warm the hearts of masters and scholars alike, little good can be expected from any kind of learning, and considerable harm will often be the consequence.
Source: Divini Illius Magistri (Vatican.va)