But if their parents can’t interrupt their shift at the factory or the Fuddruckers to pick up kids, what are the children of less-fortunate parents doing? Given that researchers have found a strong link between lower socioeconomic status and high absenteeism, it seems likely that some of them have not gone to school at all.

Applied economist Michael Gottfried, now at the University of Pennsylvania, called this idea perfectly plausible. And he would know: His research into the causes and consequences of absenteeism in America’s schools has been cited just about everywhere. It also has transformed him into an unabashed bus booster.

“I believe the bus is a lifeline for students,” he told us.