heritability of IQ at around 0.5

Heritability of IQ has nothing whatever to do with malleability (or, if you prefer this terminology, controllability) of human intelligence. That point has been made by the leading researchers on human behaviorial genetics in their recent article that I cited in the first reply to this submission on HN. It is a very common conceptual blunder, which should be corrected in any well edited genetics textbook, to confuse broad heritability estimates with statements about how malleable human traits are. The two concepts actually have no relationship at all. Highly heritable traits can be very malleable, and the other way around. It looks like the author of the new book mentioned in the submitted article has gathered a lot of evidence about malleability of human intelligence, which I will check as I read the book. (I've read other writings on this subject, and regularly participate in scholarly discussion of the latest research on this with Ph.D. psychologists.)

Intelligence, to be useful, must be used effectively.

I do agree with this point.