At the time, we were in a rather ... low-end school district. It wasn't the worst, but declining. My parents (and others) were lobbying (for years) for some sort of program for gifted students - nothing existed in our school system at the time. There were programs in
other schools - even in the same county - but not our end of the county (not poverty area, but nowhere near the 'rich' side of things, and not really quite 'middle class', looking back at things as an adult).
You're not wrong though - certainly environment has to play a factor. Diet and health probably have to have an impact in some capacity as well.
I did have a 2 parent family (up until 17, anyway!), and a supportive extended family who valued education. The school system itself was pretty deficient, and we moved later (5th grade for me), so my younger brothers had access to 'better schools' pretty much from day 1.
I also did have an interesting of reading which was nurtured early on; trips to the library were probably more fun than trips anywhere else, and I remember getting really excited when learning that the "you can only take 2 books" was just something the parents imposed - you could really take out many more at any one time(!)
Part of the claim of the post above was that IQ can 'change' - seemingly dramatically - just based on study/prep/exercises/practice (that's how I read the piece anyway). My own experience tells me that whatever change happens is likely not as impactful or longlasting as one might first assume.
IQ certainly isn't everything. I've learned that many times over the years. Much like income, over a certain particular number, for most people, there's diminishing returns re: value. Having an IQ score were 120 is on the high end, vs, say, 85 on the low end - yes, that can be advantageous. Moving that same score to, say, 128... probably not all that noticeable or useful for most people in most walks of life. Hesitating to use specific numbers because I know different tests use different scoring scales.