Education is another example. There's evidence poverty is a better indicator of educational achievement than race.
"According to a 2011 research study by Stanford sociologist Sean Reardon, the test-score gap between the children of the poor (in the 10th percentile of income) and the children of the wealthy (in the 90th percentile) has expanded by as much as 40% and is now more than 50% larger than the black-white achievement gap -- a reversal of the trend 50 years ago," Sarah Garland writes for The Atlantic.
"Underprivileged children now languish at achievement levels that are close to four years behind their wealthy peers."
Four years behind their peers.
Just because of their income.
That challenges the very notion of who we are as Americans.
We see ourselves as a middle-class country -- a place where anyone can work hard and succeed. And many do. We're a country of fighters.
But it's become more difficult for the non-rich to make it.
The country has made great strides toward racial equality since the March on Washington for Jobs and Freedom. But, in the 50 years since King's speech, economic justice seems to have become the more distant dream.