Earlier quoted context omitted.
A better analogy is height. Given some minimal level of nutrition, a child's adult height can be extrapolated quite accurately from their parents' genomes. However, if a child grows up in abject poverty, all bets are off. See Judith Rich Harris' The Nurture Assumption [1] for details. [1] http://en.wikipedia.org/wiki/The_Nurture_Assumption
However we barely understand the genetic factors. In humans it can be pretty difficult to control the environment. And then we assume we can understand the genetics of intelligence, when we barely understand either genetics or intelligence itself.
Have you heard of GWAS? They've had some major breakthroughs over the past few years, and have recently had some interesting results with regard to educational attainment. From Science:
https://www.sciencemag.org/content/340/6139/1467.abstract
If you want some more information, here's a good article from early 2012 summarizing the previous five years of findings: