For the time being, I've decided that education is to do with practical intellect, like prudence or art. In other words, thinking about education can be done purely speculatively, but educating someone will always come down to doing (and in corollary, "not-doing") -- active and passive methods.
Benjamin Franklin said that while one person is standing indecisively between two educational methods and trying to decide which is best, another person will have time to use either or both and actually cause something to happen. Marva Collins said: Anything works if the teacher does. That sort of sums up the active part.
As for the passive part -- passive has a bad rap nowadays of course, but it has a legitimate pedigree. It means the receptive side of activity. For example, the reference to Jesus's "Passion" doesn't refer to how He was feeling when He was crucified, which is what I made of it when I was a small child and heard the term, but to the undergoing of something.
Charlotte Mason talks much about masterly inactivity, and "despising not, offending not, hindering not" the children, which is so often done in the name of "educating" them. There is a season to stand back, to receive, to respond, if you want to be effective in action.
Either way, "active" or "passive" can both be supportive of education. The educator's role is secondary to that of the learner though; almost every effective means of education makes mention of that essential truth. Cicero says:
Natural ability without education has more often attained to glory and virtue than education without natural ability.
That is, I think, why pure unschooling CAN work (ie result in a well educated child who is prepared to live a reflective, reasoned adult life) but pure teacher-directed education almost never works. Indeed, it doesn't exist. There are always corners in the day where the child can be free with his own thoughts and actions. That is to say, there is always an unschooling component, but it is rarely acknowledged by the modern institutional method or considered as the foundation for academic learning that it really is.
Cardinal Newman says (speaking of modern-method schooling):
Nay, self-education in any shape, in the most restricted sense, is preferable to a system of teaching which, professing so much, really does so little for the mind.
So lots of times mechanized schooling, by not acknowledging the primary role of the learner, actually hinders learning. (If you want to read more about that, The Wundter of it All by Richard Mitchell and Against School by John Taylor Gatto are interesting to read, and so is John Newman's Knowledge viewed in Relation to Learning)
Of course, unschooling doesn't work if it is conceived as complete liberty for the child. That too is impossible. No one lives in a vacuum; everyone is influenced by the time and place they live in. But I have never heard a thoughtful unschooler proclaim that she provides a vacuum for her kids or that this would be a good thing. Even (or especially) the most radical unschoolers don't claim that; almost the opposite. See the article Mindful Parenting by Ren Allen and Sandra Dodd, and there are plenty of others.
Real unschooling is about acknowledging the child's primary role in his learning process, and respecting that and supporting that. But it's only part of the picture, because really, unschooling in that form is parenting. ... trying to parent reflectively and lovingly and personally, rather than relying on ingrained reflexes, or rules designed by someone else, or one's own less honorable impulses. The other truth connected with that is that there is so much more to life and learning than "school" or "schooly subjects". If you read The Three Stages of Unschooling, you see that for unschoolers, "schooly" stuff starts taking a back seat. You no longer have to cram little bits and pieces of daily life into boxes that say "math" or "language arts" (something I hate), because you realize that learning is a genuine and inevitable part of living as humans -- as Cicero said:
Our minds possess by nature an insatiable desire to know the truth.
Aristotle says something similar:
ALL men by nature desire to know.
I was going to bring in the island, but if I do this post will go on forever. So that part will have to wait.