A Salvadoran flag wrapped around his neck to block out the sun, Geremias Romero hunches low to the ground alongside the other laborers, following the tractor along rows of cantaloupes.

He reaches into the leafy green rows of fruit, touches a melon to gauge its ripeness, and then tosses it into a cart, where another laborer boxes it. Walk, pick, toss. The pattern goes on all morning.

Harvesting cantaloupes for $8.25 an hour isn’t the job that Romero, 28, dreamed of as a child. Born in Newark, N.J., to immigrant parents from El Salvador, he graduated from high school and has taken classes at the Art Institute of Philadelphia and Merced Community College. He has experience as a special education teacher but, unable to find...