30 Added to all this, God and Jesus Christ, as well as His doctrines, were banished from the school. As a sad but inevitable consequence, the school became not only secular and non-religious but openly atheistical and anti-religious. In such circumstances it was easy to persuade poor ignorant children that neither God nor religion are of any importance as far as their daily lives are concerned. God's name, moreover, was scarcely ever mentioned in such schools unless it were perchance to blaspheme Him or to ridicule His Church. Thus, the school forcibly deprived of the right to teach anything about God or His law could not but fail in its efforts to really educate, that is, to lead children to the practice of virtue, for the school lacked the fundamental principles which underlie the possession of a knowledge of God and the means necessary to strengthen the will in its efforts toward good and in its avoidance of sin. Gone, too, was all possibility of ever laying a solid groundwork for peace, order, and prosperity, either in the family or in social relations. Thus the principles based on the spiritualistic philosophy of Christianity having been obscured or destroyed in the minds of many, a triumphant materialism served to prepare mankind for the propaganda of anarchy and of social hatred which was let loose on such a great scale.
Source: Ubi Arcano Dei Consilio (Vatican.va)