Also - just because terrible environment vs. 'not terrible' environment makes a big difference in IQ score doesn't mean that there will be any difference between 'good' and 'terrific' environment.
I would guess that there would be, though. Is there a good reason to think differently? I would think that IQ response to environment (including teaching) would be on a continuum, but that the devil would be in the details (e.g. some teaching may not foster intelligence well and so may not be "terrific" for that, even though it is "terrific" for teaching rote knowledge).
Environmental effects on IQ would of course not just truncate abruptly. I can't think of a reason why environmental effects would just peter off, so it doesn't make sense to me to assume that.
As a complete newbie I found this page interesting:
http://en.wikipedia.org/wiki/Heritability_of_IQMaybe a better-than-adequate environment can affect some types of intelligence more than others.
http://en.wikipedia.org/wiki/Fluid_and_crystallized_intelligenceSmart drugs are another possible topic of interest here, although I am less interested in that.
