The causes of skewed distributions of outcomes are many.
"In recent times, virtually any disparity of outcomes is almost automatically blamed on discrimination, despite the incredible range of other reasons."
Note: Thomas Sowell taught economics at Cornell, UCLA, Amherst and other academic institutions. Currently, Sowell is a scholar in residence as a Senior Fellow at the Hoover Institution, Stanford University. I first noticed him when I read Dismantling America in 2010. Also, he wrote Wealth, Poverty and Politics 2016. His most recent book is Discrimination and Disparities 2018. Gerald P. O'Driscoll, Jr., Senior Fellow, Cato Institute, writes, “In this provocative book, Thomas Sowell turns the table on those who automatically link disparate outcomes to discrimination. He begins by focusing instead on the myriad of factors that need to come together for success." Read the book.
What irks me as a teacher is that divergence in education is now called discrimination, and that achievement is now called privilege. It is typical liberal rhetoric that is offensive to all hard-working students who achieve, including students of color. Sowell points out, regrettably, that "in recent times, virtually any disparity of outcomes is almost automatically blamed on discrimination, despite the incredible range of other reasons." (Sowell calls it the invincible fallacy. I call it a sham when scholarship and achievement are criticized with empty rhetoric.)
The social vision and rhetoric of progressives "treat beliefs as sacred dogmas beyond the reach of evidence or logic." Facts don't matter much! "Facts seem to have become irrelevant, for all too many people, who rely instead on visions and rhetoric."
Also, the idea that inputs do not influence outputs is another issue. Of course, they do! Sowell explains, "To admit that inputs affect outputs, whether in education in the economy or other areas, would be to undermine the [social] vision and agenda" [of progressive ideology]. According to Sowell, the invincible fallacy is that "outcomes in human endeavors would be equal, or at least comparable or random, if there were no biased interventions, on the one hand, nor genetic deficiencies, on the other." The invincible fallacy assumes "an even or random distribution of outcomes in the absence of such complicating causes as genes or discrimination." The assumption, of course, is wrong!
The causes of skewed distributions are many. Indeed, life, itself, is unfair, yet "fallacies of fairness" abound in our classrooms. All students get the same instruction under Common Core and state standards regardless of their math achievement, which should drive outcomes to be the same. Not Really! It is wishful thinking. Outcomes would not be the same. The crux is that even if the inputs were the same, which I doubt would be possible, the outputs would still not be the same! As Sowell says, "Equal inputs does not produce equal outputs."
Incidentally, one of the many consequences of the invincible fallacy has been the "dumbing down of education."