"Hence every form of pedagogic naturalism which in any way excludes or weakens supernatural Christian formation in the teaching of youth, is false. Every method of education founded, wholly or in part, on the denial or forgetfulness of original sin and of grace, and relying on the sole powers of human nature, is unsound. Such, generally speaking, are those modern systems bearing various names which appeal to a pretended self-government and unrestrained freedom on the part of the child, and which diminish or even suppress the teacher's authority and action, attributing to the child an exclusive primacy of initiative, and an activity independent of any higher law, natural or divine, in the work of his education.
If any of these terms are used, less properly, to denote the necessity of a gradually more active cooperation on the part of the pupil in his own education; if the intention is to banish from education despotism and violence, which, by the way, just punishment is not, this would be correct, but in no way new. It would mean only what has been taught and reduced to practice by the Church in traditional Christian education, in imitation of the method employed by God Himself towards His creatures, of whom He demands active cooperation according to the nature of each; for His Wisdom "reacheth from end to end mightily and ordereth all things sweetly."
Pope Piux XI writes this in
He also writes:
"Nor will this necessary caution, suggested also by the pagan Quintilian, in any way hinder the Christian teacher from gathering and turning to profit, whatever there is of real worth in the systems and methods of our modern times, mindful of the Apostle's advice: "Prove all things: hold fast that which is good." Hence in accepting the new, he will not hastily abandon the old, which the experience of centuries has found expedient and profitable."
This seems to give a cautious go-ahead to some innovation and pedagogical exploration when not contradictory to sound and traditional principles.
One thing that seems to me to support some form of unschooling (as opposed, possibly, to experimental, alternative schools based on child-directed learning)is the regard the Church has always had for family-based education and its informal, yet painstaking methods of teaching and training children.
This seems to make a claim for the crucial importance of environment and good example within the family as a foundation for genuine learning. And that is very close to what I believe "successful" unschoolers (as opposed to the ones who basically unparent as well as unschool) base most of their education upon.
In fact, I would argue that these two are fundamental principles for any kind of successful education -- that the "structured" homeschoolers and the people who send their kids to school, and have success in academic and character terms, base their educational structure on the same principles.
To use a social example, it is acknowledged that poverty alone does not lead to academic problems among the economically disadvantaged; it is poverty + family breakdown, the latter leading to poor example and poor environment (as Pope Pius mentions).
One more quote from this very beautiful and rich encyclical on Christian Education:
"Now all this array of priceless educational treasures which We have barely touched upon, is so truly a property of the Church as to form her very substance, since she is the mystical body of Christ, the immaculate spouse of Christ, and consequently a most admirable mother and an incomparable and perfect teacher. This thought inspired St. Augustine, the great genius of whose blessed death we are about to celebrate the fifteenth centenary, with accents of tenderest love for so glorious a mother:
"O Catholic Church, true Mother of Christians! Not only doest thou preach to us, as is meet, how purely and chastely we are to worship God Himself, Whom to possess is life most blessed; thou does moreover so cherish neighborly love and charity, that all the infirmities to which sinful souls are subject, find their most potent remedy in thee. Childlike thou are in molding the child, strong with the young man, gentle with the aged, dealing with each according to his needs of mind of body. Thou does subject child to parent in a sort of free servitude, and settest parent over child in a jurisdiction of love. Thou bindest brethren to brethren by the bond of religion, stronger and closer then the bond of blood .... Thou unitest citizen to citizen, nation to nation, yea, all men, in a union not of companionship only, but of brotherhood, reminding them of their common origin. Thou teachest kings to care for their people, and biddest people to be subject to their kings. Thou teachest assiduously to whom honor is due, to whom love, to whom reverence, to whom fear, to whom comfort, to whom rebuke, to whom punishment; showing us that whilst not all things nor the same things are due to all, charity is due to all and offense to none."