Last week’s disappointing unemployment report has refocused attention on the question of why, despite modest signs of economic recovery in recent months, American companies aren’t hiring. Indeed, some of the most puzzling stories to come out of the Great Recession are the many claims by employers that they cannot find qualified applicants to fill their jobs, despite the millions of unemployed who are seeking work. Beyond the anecdotes themselves is survey evidence, most recently from Manpower, which finds roughly half of employers reporting trouble filling their vacancies. The first thing that makes me wonder about the supposed “skill gap” is...