In South Sudan, where hundreds of thousands are on the brink of starvation and famine has been declared in two counties, children are struggling to learn because of lack of food.

"I can't do my homework because I'm hungry," Thor Athiam says. "I can't concentrate."

He shuffles the dirt under his small bare feet. The skinny 9-year-old's ripped shirt falls loosely off his frame. Crouched under a tree outside his classroom, he waits patiently for lunch.

This will be the first time he's eaten since yesterday.

"This is the worst year for school dropouts," says Deng Mawien, the deputy headmaster in the school in this small town. "The hunger is having a negative impact."

Out of 1,000 children enrolled, Mawien says roughly 700 show up daily. Some have left with their families to neighbouring Sudan, while others are sent by their parents to work in the market to make money for food.

South Sudan's three-year civil war and economic crisis has disrupted farming so much that millions of people are going hungry, aid officials say.

As part of an initiative to keep kids in school, World Vision says it is providing 30,000 students with one hot meal a day in 171 schools in Greater Bahr El Ghazal province.

"When the kids come to school in the morning and see the fire cooking, their eyes light up," says Matthew Majok, a volunteer teacher. He says 14 of the 16 children who come to his class every morning haven't had anything to eat.

"I see their faces," he says. "They're hungry and they don't want to listen."

For most students, this is the only meal they'll eat all day.

Devouring his lunch of porridge in a small metal bowl, 9-year-old Athiam says he's determined to continue his studies because he wants to become a teacher.

"If you teach other generations they can teach the next ones," he says. "And then there will be no hunger."