She nodded, solemn as a judge. Her mother mouthed "thank you" —two words Carlos never got tired of hearing.

At the next stop, a middle-schooler named slumped onto the bus, earbuds in, not making eye contact. But Carlos noticed his shoes were untied. "Jay. Laces, man. I don’t need you tripping into my stepwell."

Not a loud roar, but a deep, diesel-powered vibration that rolled across the sprawling Northside Independent School District—from the Hill Country edges near Helotes to the steady blocks of Leon Valley. It was the sound of 475 buses waking up.