The school serves residents of Matamoros, a dusty, sunbaked city of 489,000 that is a flash point in the war on drugs. There are regular shoot-outs, and it's not uncommon for locals to find bodies scattered in the street in the morning. To get to the school, students walk along a white dirt road that parallels a fetid canal. On a recent morning there was a 1940s-era tractor, a decaying boat in a ditch, and a herd of goats nibbling gray strands of grass. A cinder-block barrier separates the school from a wasteland—the far end of which is a mound of trash that grew so big, it was finally closed down. On most days, a rotten smell drifts through the cement-walled classrooms. Some people here call the school un lugar de castigo—"a place of punishment."

For 12-year-old Paloma Noyola Bueno, it was a bright spot. More than 25 years ago, her family moved to the border from central Mexico in search of a better life. Instead, they got stuck living beside the dump.