5 There is another point upon which those will agree with us who differ from us in everything else; it is not by means of a purely scientific education and with vague and superficial notions of morality that Catholic children will leave school such as the country desires and expects. Other serious and important teaching must be given to them if they are to turn out good Christians and upright and honest citizens; it is necessary that they should be formed on those principles which, deeply engravers on their consciences, they ought to follow and obey, because they naturally spring from their faith and religion. Without religion there can be no moral education deserving of the name, nor of any good, for the very nature and force of all duty comes from those special duties which bind man to God, who commands, forbids, and determines what is good and evil. And so, to be desirous that minds should be imbued with good and at the same time to leave them without religion is as senseless as to invite people to virtue after having taken away the foundations on which it rests. For the Catholic there is only one true religion, the Catholic religion; and, therefore, when it is a question of the teaching of morality or religion, he can neither accept nor recognize any which is not drawn from Catholic doctrine.
Source: Affari Vos (Vatican.va)