From what I know, there are high correlations between an individual's IQ test scores at different times, especially in the short run. Depending on the study, it ends up being something like 0.95 in the short run and 0.7-0.9 between different ages (I'm just quoting rough ballpark figures from memory -- they of course differ between studies and age spans). Some impressively high correlations were found even in a study that compared test scores of a group of individuals at 11 and 77 years of age.
On the other hand, people can be coached to significantly improve their IQ test scores. At least so says Rushton, of all people.
Then of course, as with all issues where you might want to make some sense of what IQ scores exactly imply, the Flynn effect throws a wrench into any attempt to come up with a neat, plausible, and coherent theory.
But even regardless of all this, one should still not forget that the connection between IQ and any realistic measure of success is itself just probabilistic. This is especially true for high-scoring individuals: instead of worrying whether one's score is 120, 130, 140, or whatever, one would be better advised to worry about whether one is deficient in other factors important for success and accomplishment in life.
On the other hand, people can be coached to significantly improve their IQ test scores. At least so says Rushton, of all people.
I'd point out that this should be extremely obvious a point, given how some subtests are Gc-loaded. You can 'improve' your IQ by studying some vocab, quite aside from the usual practice effects.
(And one of the standing questions about dual n-back is whether it doesn't (partially) amount to training for matrix-style Gf IQ tests.)
I am beginning to suspect that it is surprisingly common for intelligent, competent adults to somehow make it through the world for a few decades while missing some ordinary skill, like mailing a physical letter, folding a fitted sheet, depositing a check, or reading a bus schedule. Since these tasks are often presented atomically - or, worse, embedded implicitly into other instructions - and it is often possible to get around the need for them, this ignorance is not self-correcting. One can Google "how to deposit a check" and similar phrases, but the sorts of instructions that crop up are often misleading, rely on entangled and potentially similarly-deficient knowledge to be understandable, or are not so much instructions as they are tips and tricks and warnings for people who already know the basic procedure. Asking other people is more effective because they can respond to requests for clarification (and physically pointing at stuff is useful too), but embarrassing, since lacking these skills as an adult is stigmatized. (They are rarely even considered skills by people who have had them for a while.)
This seems like a bad situation. And - if I am correct and gaps like these are common - then it is something of a collective action problem to handle gap-filling without undue social drama. Supposedly, we're good at collective action problems, us rationalists, right? So I propose a thread for the purpose here, with the stipulation that all replies to gap announcements are to be constructive attempts at conveying the relevant procedural knowledge. No asking "how did you manage to be X years old without knowing that?" - if the gap-haver wishes to volunteer the information, that is fine, but asking is to be considered poor form.
(And yes, I have one. It's this: how in the world do people go about the supposedly atomic action of investing in the stock market? Here I am, sitting at my computer, and suppose I want a share of Apple - there isn't a button that says "Buy Our Stock" on their website. There goes my one idea. Where do I go and what do I do there?)