In 2012, I read an article on Breitbart.com that called out liberal bias in the teaching of economics. The author pointed to “distortions” in a high school textbook co-authored by Paul Krugman that dismissed the thinking of supply-side economists. It denied that the tax reduction they helped bring about during the Reagan administration had any effect on economic growth—despite government data showing exactly the opposite: a dramatic surge in job creation and a marked decline in unemployment. The author declared, “If a student were to submit an essay with such disregard for basic evidence, it would ensure a failing grade.”...