The recent growth of online education has been astounding. Last year, 35 million people signed up for at least one online class. That’s more than double the previous year’s enrollment. The popularity of online learning is easy to understand. Today, students have access to well over 4,000 courses in a wide array of subjects, from chemistry to philosophy to graphic design. They participate at a time and place that suits their schedule. Many courses are free. There is, however, a seriou