The University of Pennsylvania’s Wharton is genuinely regarded as one of the finest business schools in the country — U.S. News & World Report ranks it second, behind only Stanford. But these aspiring giants of the business world could use an education in real-world economics. Nina Strohminger, a professor of legal studies and business ethics, tweeted that she had asked students what the average American makes. They did not do well. The tweet triggered a firestorm of responses, mostly along the lines that these students were out of touch. One Twitter user linked to New York Times data, showing the...