4 AM. The school halls are still dark. A custodian pushes the wide mop. The hum of the floor buffer echoes. Shoulders ache from the long sweep. Median pay for this work: $35,660 a year. Over 500,000 people do this in US schools. Kids don’t see the early light. Teachers don’t know the quiet effort. But if that person stopped coming, the whole building would feel it. This country runs on hands like those.