Haley Nordeen, 19, is spending the entire summer at the Prodesenh center in San Mateo Milpas Altas, Guatemala. The American University student helped build the center's new library. Carrie Kahn/NPR hide caption

itoggle caption Carrie Kahn/NPR

Jackson Merrick, a sixth-grader from McLean, Va., says he donates half of his allowance to charity. Morgan Walker/NPR hide caption

itoggle caption Morgan Walker/NPR