There are at least two different ways of getting someone to learn something. You can offer to teach him something he wants to know, or you can compel him to learn something you want him to know. Unschooling uses the first approach, conventional schooling the second. One difference between the two is their effect on the incentives of teachers.
Consider the case of literacy. The ability to read is useful to almost everyone in a modern society, so one would like an educational system that does a good job of teaching it. It is widely believed that the current American system does not.
If the objective is to teach people to read, the obvious starting point is to ask what sorts of things those people would enjoy reading, since it is easier to get someone to do something he likes doing. The answer might be comic books, car magazines, science fiction, fantasy, soap opera summaries, or any of a wide variety of other sorts of written material, depending on the particular people being taught.
As best I can tell, that is not the approach taken by conventional K-12 schooling. Instead, students are assigned to read books chosen on one of two criteria. Either they are books regarded as good literature—famous books from the past or current books that English professors approve of—or books believed to teach lessons that the people selecting the books want taught. That would include biblical literature in the past, patriotism—or acceptance of homosexuality, depending on the state—at present, and a wide range of other lessons, depending on current and local political fashion. While it is always possible that the books chosen would also be ones students enjoyed—I'm very fond of Kipling, some of whose stories might be assigned reading in English class—that is not what they would be chosen for, so the odds are not very good.
The ability to read is useful to almost everyone. Knowledge of and appreciation for great literature, even if we accept the educational establishment's definition of what qualifies, no doubt can enrich one's life, but on the evidence of what books people actually read it does not enrich the lives of a very large fraction of the population. That suggests that learning the former should probably have considerably higher priority than learning the latter.
In an educational environment where teachers can advise and persuade pupils but not compel them, it will, because the teachers who insist on telling their pupils to read books that the teacher likes and the pupil does not will shortly find their advice ignored. In an environment where teachers can tell students what books to read and, to at least some degree, punish those who fail to obey, on the other hand, there will be a strong temptation to assign the books that the teacher thinks the student ought to read, sacrificing the higher priority of literacy for the lower priority of literature—or, sometimes, propaganda.
Which may explain why Johnny can't read.
I encountered a different version of the same logic a good many years ago in my own work. My Price Theory textbook was out of print. I decided to rewrite it into a book targeted at the proverbial intelligent layman, the sort of book that gets read for the fun of it while teaching the reader the basics of an academic subject, in my case economics. My model, insofar as I had one, was The Selfish Gene, a book from which I learned quite a lot about evolutionary biology.
In the course of the project, it occurred to me that there was an important difference between the book I was starting with and the book I intended to end with; nobody would be forced to read the latter. It followed that if at any point the reader decided that it was not worth continuing, I would lose him. To deal with that problem I followed a deliberate policy of starting each chapter with a hook, a puzzle that would sufficiently engage the reader to persuade him to finish the chapter to find the solution. Economics is full of such puzzles; I don't know how hard it would be to do the same thing in another field.
The result, Hidden Order: The Economics of Everyday Life, has been by a sizable margin my most successful book.
Incentives matter—including mine.
In the interest of honesty, I should add that some people are forced to read Hidden Order, because it is occasionally used as a textbook, even though that was not the purpose it was written for. But not, I think, very many people.