Sometimes I hear:
"Don't force kids to learn abstractions which they won't use. Teach them practical things. That's what they want to learn."
I'm listing this as one fallacy, but it contains at least five blunders, which I'll enumerate after the jump.
1) Educaation is an end, not (primarily) a means. We learn because learning is enjoyable. Curiosity is as basic a drive as hunger or lust. Without curiosity, our ancestors would have died out long before the caves.
Remember the story: There were two trees in the Garden of Eden, one was the Tree of Life; Adam and Eve decided to eat from the Tree of Knowlege. Feed the kids' curiosity.
2) Abstractions clarify. Your mind is like your hands: you can't carry a dozen loose egs; put them in a box and it's esy.
Similarly, you cut your time spent learning addition tables in half when you figure out that 7 + 5 = 5 + 7. (When I was young, my father told me that 'Algebra is the lazy man's arithmetic.' That's true, and it fueled a lot of my interest in mathematics. You'd be surprised how small a fraction of the American public can multiply 75 times 85 in their heads. Anybody who remembered Freshman algebra can.)
Studies have been made on Chess masters' ability to remembwer positions. Put an actual game in front of one, give him a brief glance, and then hide it. He'll tell you where every piece is. Scatter some chessmen across a board, and he'll remember no better than the average man. Chess masters don't remember where each piece is; they remember what the possibilities of play -- the threats and opportunities are.
You're the same way. Can you remember a thousand letters chosen at randon? Can you remember a poem containing several thousand letters?
3) For that matter, people who tell you: "That's fine in theory, but -- in practice ..." are almost always spouting a new theory. It's just, when people say that to me, a theory which hasn't been tested.
4) Actually, we haven't the faintest idea what learning will be of practical value when today's gradeschoolers are working adults. "Why teach them about Mesopotamia? They'll never have to know that." I spent hours learning to use trig tables and the sliderule. Of all the "useless" information I've absorbed during my life, I make the least use of that "practical instruction."
5) This is also what psychologists call "projection." It's not that kids want to learn 'something practical.' Most of the practical instruction we impart is only useful so much later in life that it is beyond the kids' horizon. The difference between ballancing a checkbook and calculating the orbit of the moon is in our heads. Johnny's life doesn't include either.