"Restriction Of Range:" It's Not Just A Statistical Problem, It's A Desirable Lifestyle

From Quartz:
By Miles Kimball and Noah Smith October 27, 2013 
Miles Kimball is an economics professor at the University of Michigan. He blogs about economics, politics and religion. 
Noah Smith is an assistant professor of finance at Stony Brook University. His blog is Noahpinion.

“I’m just not a math person.”

We hear it all the time. And we’ve had enough. Because we believe that the idea of “math people” is the most self-destructive idea in America today. The truth is, you probably are a math person, and by thinking otherwise, you are possibly hamstringing your own career. Worse, you may be helping to perpetuate a pernicious myth that is harming underprivileged children—the myth of inborn genetic math ability.
Is math ability genetic? Sure, to some degree. Terence Tao, UCLA’s famous virtuoso mathematician, publishes dozens of papers in top journals every year, and is sought out by researchers around the world to help with the hardest parts of their theories. Essentially none of us could ever be as good at math as Terence Tao, no matter how hard we tried or how well we were taught. But here’s the thing: We don’t have to! For high school math, inborn talent is just much less important than hard work, preparation, and self-confidence.

How do we know this? First of all, both of us have taught math for many years—as professors, teaching assistants, and private tutors. Again and again, we have seen the following pattern repeat itself:

Different kids with different levels of preparation come into a math class. Some of these kids have parents who have drilled them on math from a young age, while others never had that kind of parental input. 
On the first few tests, the well-prepared kids get perfect scores, while the unprepared kids get only what they could figure out by winging it—maybe 80 or 85%, a solid B. 
The unprepared kids, not realizing that the top scorers were well-prepared, assume that genetic ability was what determined the performance differences. Deciding that they “just aren’t math people,” they don’t try hard in future classes, and fall further behind. 
The well-prepared kids, not realizing that the B students were simply unprepared, assume that they are “math people,” and work hard in the future, cementing their advantage. 
Thus, people’s belief that math ability can’t change becomes a self-fulfilling prophecy.
Sure. No doubt that's part of the story.
On the other hand, high school math students aren't restricted to just: 
1. "the well-prepared kids [who] get perfect scores"

High school math student
2. "the unprepared kids [who] get only what they could figure out by winging it—maybe 80 or 85%, a solid B"
There are more levels of high school math students in heaven and hell than are dreamt of in your philosophy, Noah.

P.S. Robert VerBruggen correlates algebra grades and scores on the ASVAB military entrance exam here.