Here is a “mea culpa” from Nick Hanauer, an entrepreneur and venture capitalist who made his fortune in technology companies. Hanauer gave much money to transform schools so that they could become engines of equity erasing economic and social inequalities (and poverty as well) that bedevil American society.

Long ago, I was captivated by a seductively intuitive idea, one many of my wealthy friends still subscribe to: that both poverty and rising inequality are largely consequences of America’s failing education system. Fix that, I believed, and we could cure much of what ails America.

This belief system, which I have come to think of as “educationism,” is grounded in a familiar story about cause and effect: Once upon a time, America created a public-education system that was the envy of the modern world. No nation produced more or better-educated high-school and college graduates, and thus the great American middle…