Sometimes--especially as our progeny get older and we get into that mess of categories known as "credits"--it's tempting even to pass on a good book that doesn't fit nicely into one of those categories. Biographies can fall in there with the uncategoricals--and they're often the best books we read! (Is Plutarch a subject?) We can't break knowledge down into spoon-size bits and decide what goes in the mouth when. (Charlotte Mason referred to that as the horse that gets one bean a day.)
My own school was supposedly into unit studies, interconnectedness and all that progressive 1970's stuff (learning centers with headphones, open-ended "activity cards", and few textbooks around that I can remember, other than a few rather deadly language and spelling texts). But even so, there are things I learned about without ever making connections to their wider significance. I remember playing with magnets and dutifully making diagrams of which way the iron filings went; but I didn't learn until years later that those magnets had any connection at all to electricity--not only that magnetic compasses helped explorers find the new world, but that magnets made the doorbell work. Mr. Fixit, of course, seemed to pick those things up without being told, but he was a Mr. Fixit (or a Mr. Taker-aparter) from diapers on--and he was a Boy. My own completely unproven theory is that Girls--at least those who aren't parented by a Mr. Fixit--especially need that greater interconnectedness, or they will grow up (as I did) not really understanding much about how the world works (or even how the doorbell rings).
Here's the quote which inspired Karen's post:
"One thesis, which is, perhaps, new, that Education is the Science of Relations, appears to me to solve the question of curricula, as showing that the object of education is to put a child in living touch as much as may be of the life of Nature and of thought. Add to this one or two keys to self knowledge, and the educated youth goes forth with some idea of self management, with some pursuits, and many vital interests."--Charlotte Mason