16 These are the things to ensure on this point. First, Catholics should not choose mixed schools but have their own schools especially for children. They should choose excellent and reputable teachers for them. For an education in which religion is altered or non-existent is a very dangerous education. We often see both cases occurring in mixed schools. No one should be ready to believe that instruction and piety can be separated with impunity. In effect, if it is true that We cannot exempt ourselves from the duty of religion at any period of life, in private or public affairs, so much the less should this duty be omitted at any age which is thoughtless, in which the spirit is ardent and exposed to so many inducements to evil.
Source: Militantis Ecclesiae (Vatican.va)