LAKE WORTH, Fla. — Dayvin Mungia, 7, arrived from El Salvador at South Grade Elementary in South Florida last year with, it seemed, no schooling at all. “He didn’t even recognize the first letter of his name,” said Nicol Sakellarios, his second-grade teacher, as the smiling boy gamely stumbled through his ABC’s in summer school not long ago. “Good job, my love,” she said, prodding him on as he faltered again and again.

Laura Martin, 16, who attended school for only three years in Guatemala and speaks an indigenous language, plans to enroll in high school in Florida next month. “Illiterate” and “0” were scrawled on a math work sheet that she tried and failed to complete after she made her way across the border in May.

Migrant children arriving in record numbers are creating challenges for school districts across the country. Many of the newcomers have disjointed or little schooling; their parents, often with limited reading and writing skills themselves and no familiarity with the American education system, are unable to help.

Schools in places like Lake Worth, a city near President Trump’s Mar-a-Lago resort that has become a favorite destination for Guatemalans, are scrambling to hire new staff and add summer sessions to support the newcomers.