Extreme weather disrupted the schooling of about 242 million children in 85 countries last year — roughly 1 in 7 students, the U.N. children's agency reported Thursday, deploring what it said was an "overlooked" aspect of the climate crisis.

Heat waves had the biggest impact, the report showed, as UNICEF's executive director Catherine Russell warned children are "more vulnerable" to extreme weather.

"They heat up faster, they sweat less efficiently, and cool down more slowly than adults," she said in a statement.