What you are describing is stereotype threat. High-quality evidence for it is scarce to none; a recent meta-analysis: http://www.sciencedirect.com/science/article/pii/S0022440514....

The evidence for poverty affecting education performance, however, seems pretty high here. Example paper out of many: http://www.academicjournals.org/article/article1379765941_La...

And there's more too it, of course. I chose this link primarily because I found another observation very interesting: "In many studies, [the] mother’s education [level] had a more significant effect on children’s scores than income."

Equating inborn aptitude to SAT scores alone seems very short-sighted.

The interesting thing about the study you cite is that it only focuses on children and adolescents. You fail to mention that the majority of research has been carried out in college student populations and the findings are fairly robust. One resource for dozens of articles is the bibliography at reducingstereotypethreat.org; since you seem to be down on it I'll just link straight to their discussion of criticisms of stereotype threat [1].

However, stereotype threat is not the only mechanism that fits the poster's description. Most Americans, upon hearing that I'm a mathematician, say, "I hate math! and I suck at it." Then they stare at me hostilely or say, "You must be really smart." There's a little subset of 40-65 year old women, though, who say wistfully, "I loved math and it was my best subject... but... in high school they said I wouldn't need it so I couldn't take the calculus class, I had to take typing instead..." Tracking in high school is used extensively and dissuades people tracked into crappy high school STEM classes from pursuing STEM degrees in college (or getting in at all).

[1] http://www.reducingstereotypethreat.org/criticisms.html

That's not just stereotype threat - to give an example, there are people I know in their early 20s who were strongly discouraged from doing higher level maths in high school, and as a result, had a much harder university level maths experience.