BOGOTÁ, Colombia—Paola Hernández, an unemployed single mother of three who lives in a hillside shanty here, doesn’t have a working internet connection for her children’s online classes or the money to print out homework assignments.

The result is that for 15 months—since the school nearby closed because of the pandemic—her kids have had no classroom education. Her 16-year-old daughter Wendy will have to repeat the sixth grade. Her 8-year-old son Johan can’t read his own name.

“My children are falling so far behind,” said Ms. Hernández, 31 years old, who held back tears explaining how she has had to beg on the streets while struggling to find work as a housecleaner. “I cry when I think about what kind of future I’m leaving for these kids.”

Ms. Hernández’s anguish is part of the generational catastrophe unfolding across Latin America, where children on average have missed more school days during the pandemic than anywhere else in the world, according to Unicef. More than half of the region’s 190 million school-age children remain out of the classroom, many with no viable options for remote learning.

The World Bank estimates that some 15%, or 28 million school-age children, will drop out altogether—troubling for a region where students had already lagged behind other parts of the world in math and reading comprehension. Education advocates and economists warn of an unprecedented blow to Latin America’s social and economic development in years to come, likely spurring poverty, violence and migration.