Study suggests that economic divide is growing rapidly between America's richest and poorest.

The Alliance for Higher Education and Democracy released a study that suggests the gap between America's richest and poorest is playing out most rapidly in higher education statistics.

In the last 40 years, the percentage of America's poorest students (those making $34,160 a year or less) who've attained a bachelor's degree by the age of 24 rose only from 6% to 9% of that entire economic class. Meanwhile, in the same time span, America's wealthiest students have now graduated by 24 at much greater rates--increasing from 44% to 77%.

The more money your family makes, the more reliably you tend to graduate college. 99% of students from America's absolutely wealthiest families (those making $108,650 or more) graduate by the age of 24.

Why the disparity? Experts can't pinpoint the reason, but one glaring fact stands out.

The average cost to attend college in 2012 is more than two times what it was in 1975--when the federal Pell Grant student assistance program was created. Back in 1975, Pell Grants covered 67% of college costs. By 2012, Pell only covered 27%. Higher costs, less assistance.

Likewise, says David Zimmerman, an economics professor at Williams College in Massachusetts, there's a gross lack of low-income students at America's most premier colleges and universities.

So that American dream you always hear about? It's still really just a dream.