As an European, I did never have any IQ test, nor I know anybody who (to my knowledge) was ever administered an IQ test. I looked at some fac-simile IQ tests on the internet, expecially Raven's matrices.
When I began to read online blogs from the United States, I started to see references to the concept of IQ. I am very confused by the fact that the IQ score seems to be treated as a stable, intrinsic charachteristic of an individual (like the height or the visual acuity).
When you costantly practice some task, you usually become better at that task. I imagine that there exists a finite number of ideas required to solve Raven matrices: even when someone invents new Raven matrices for making new IQ tests, he will do so by remixing the ideas used for previous Raven matrices, because -as Cardano said- "there is practically no new idea which one may bring forward".
The IQ score is the result of an exam, much like school grades. But it is generally understood that school grades are influenced by how much effort you put in the preparation for the exam, by how much your family cares for your grades, and so on. I expect school grades to be fairly correlated to income, or to other mesures of "success".
In a hypothetical society in which all children had to learn chess, and being bad at chess was regarded as a shame, I guess that the ELO chess ratings of 17 year olds would be highly correlated with later achievements. Are IQ tests the only exception to the rule that your grade in an exam is influenced by how much you prepare for that exam? Is there a sense in which IQ is a more "intrinsic" quantity than, for example, the AP exam score, or the ELO chess rating?
Sadly, I can only share the synthesized results of years of reading - I don't keep track of where my ideas come from (though I do try to avoid known-bad sources)
#1 is seen with SAT scores - taking the test a second time / taking a prep course improves the median student's score by ~10 percentage points. I (and others) attribute this to improvements in the "IQ test taking ability" portion of the SAT, not the "have memorized vocabulary and rules of math" portion.
#3 is clearly seen in results from twin studies, adoption studies, and just looking at the world (ie we see a wider range in "ability to do things we would predict high IQ people to be better at" among people with similar childhoods than we do among people with dis-similar childhoods in extended families.