From David Brooks How We Are Ruining America:
The educated class has built an ever more intricate net to cradle us in and ease everyone else out. It’s not really the prices that ensure 80 percent of your co-shoppers at Whole Foods are, comfortingly, also college grads; it’s the cultural codes.
Status rules are partly about collusion, about attracting educated people to your circle, tightening the bonds between you and erecting shields against everybody else. We in the educated class have created barriers to mobility that are more devastating for being invisible. The rest of America can’t name them, can’t understand them. They just know they’re there.
For many decades, David Brooks has written extensively about the so-called over-educated class and the stratification of society. But what is stopping him from packing up his stuff and moving to West Virginia, which has the lowest college graduation rate (at just 18.5%) of any state. They aren’t discussing David Foster Wallace or Pilates too much over there, I’m sure. Liberals preach inclusiveness yet spend millions of dollars to isolate themselves from the very diversity that try to impose on others. The hypocrite elitist liberal is a well-worn caricature, but an accurate one. Also, not all college grads fit into Brook’s cosmopolitanism framework: just the ones from elite schools, whereas liberal arts grads from less prestigious institutions not uncommonly find themselves with a lot of debt and mediocre, low-status job prospects. 
Again, it comes down to IQ, which explains class stratification more so than any other factor. Although David Brooks and Charles Murray discuss similar themes of class, culture, and economics in their books and articles, Charles Murray takes it step further by discussing the root cause: IQ. Social mobility, education, and IQ are corrected:
Height at midlife, years of education and childhood IQ were significantly positively related to upward social mobility, while number of siblings had no significant effect. For each standard deviation increase in IQ score at the age 11, the chances of upward social mobility increases by 69% (with a 95% confidence). After controlling the effect of independent variables, only IQ at age 11 was significantly inversely related to the downward in social mobility. Which means that more years of education help a man to surpass his father’s social class, and that low IQ makes a man prone to fall behind his father’s social class.
The reason why so many studies show stagnant mobility is because such studies don’t account for IQ and use real wages instead of nominal wages. Because real wages rose up until the mid-70’s, earlier generations will show more mobility.
Because IQ and education are so highly correlated, one could just replace the words ‘education/educated’ with ‘IQ’ and Mr. Brook’s article would be equally valid.
As discussed here, a higher percentage of children born into the lowest quintile of family wealth but complete college are more likely to advance to the top quintile, than the percentage of dropouts who are born into the top quintile and then stay in the top quintile as adults.
As shown below, college graduates born into the second quintile have a 37% chance of entering the top quintile, whereas high school graduates born into the top quintile have only a 25% chance of staying there as adults:
From Steve Hsu Income, wealth, and IQ, who shows there is a positive correlation between AFQT scores (a proxy for IQ) and upward mobility:
This last figure is very problematic for the “Social Status/Wealth causes IQ” position. It seems to be the other way around: the kids escaping bottom quintile childhoods all experienced poverty, but the ones with higher cognitive ability were more likely to move up. (Recall that adopted children tend to resemble their biological parents much more than their adoptive ones; family environment has a limited effect on IQ, which is highly heritable.)
Pew: Individuals with higher test scores in adolescence are more likely to move out of the bottom quintile, and test scores can explain virtually the entire black-white mobility gap. Figure 13 plots the transition rates against percentiles of the AFQT test score distribution. The upward-sloping lines indicate that, as might be expected, individuals with higher test scores are much more likely to leave the bottom income quintile. For example, for whites, moving from the first percentile of the AFQT distribution to the median roughly doubles the likelihood from 42 percent to 81 percent. The comparable increase for blacks is even more dramatic, rising from 33 percent to 78 percent. Perhaps the most stunning finding is that once one accounts for the AFQT score, the entire racial gap in mobility is eliminated for a broad portion of the distribution. At the very bottom and in the top half of the distribution a small gap remains, but it is not statistically significant.
Related: The Inescapable Pull of Biology
 Although this would seem to contradict the thesis of college being a ticket to upward mobility, the wage growth differential between dropouts and college grads has only widened since 2008. College grads have seen some real wage growth since 2008, whereas dropouts have not. This is due to many middle class, medium-IQ jobs being lost in the aftermath of the crisis–jobs which have yet to return despite an otherwise strong economy and record high corporate profits and stock prices.