My take is two-fold:
1) Practice, like Ms Chua is talking about, is only possible for people who are of well above-average intelligence to begin with. I’m not sure anyone is capable of making someone with an IQ of 80 practice the violin for three hours at a time (may God be with anyone who tries). I don’t think anyone denies that practice makes people better at stuff, but I certainly deny that anyone is capable of practicing like Ms Chua’s kids. Incidentally, it also requires smart parents who are very conscientious. In sum, anyone who can practice this much is going to be a smart person from a smart family. My money is still on genetics.
2) I think people are correct to point out that Ms Chua is too strict. However, I don’t think her methodology is worse than the current practice of making sure that we don’t ever – under any circumstances – hurt a kid’s feelings (I’ll post more on this later in the week in a book review). Frankly, if I had to pick one of these two extremes, I’d be on Chua’s side. My decision would be easier when it comes to "educating" children that aren’t particularly intelligent. Telling a dumb kid that everything he does is smart is a good way to get a really dumb adult. For proof of this statement, see, e.g., contemporary America.
Finally, I’ve never met a person who was classically trained on the piano or the violin who was not exceptionally intelligent. I’m not sure which way the causality runs in this particular case, but . . .