London (CNN)Children across the globe have seen their schools closed because of the coronavirus pandemic.
According to the World Bank, 1.6 billion students were out of school during the first peak of the pandemic in April 2020, and almost 700 million remained out as 2020 drew to a close.
It may take years for the full impact of these months of missed schooling to be known, so what can history tell us about the long-term effects of disruptions to education?
Nothing can be directly compared to the impact of the coronavirus pandemic, said Alberto Posso, professor of economics at RMIT University in Melbourne, Australia, but some parallels can be drawn. "As far as learning from history goes, I think the value is in the potential warning signs these things can give us," he said.
Posso looked at examples including the Ebola epidemic in West Africa, teacher strikes in Argentina in the 1980s and World War II in a piece for The Conversation.
Perhaps the most striking data came from a paper assessing the long-term education cost of World War II for children who were 10 years old during the conflict in Germany and Austria -- both participants in the war -- and comparable children in Switzerland and Sweden, countries that remained officially neutral.
The authors of the 2004 paper, Andrea Ichino and Rudolf Winter-Ebmer, concluded that "individuals experienced a sizable earnings loss some 40 years after the war, which can be attributed to the educational loss caused by the conflict."
"Austrian children missed around 20% of classes during the war and their earnings dropped by around 3%. German children lost around 25% of classes and had earnings dropped by around 5%," Posso told CNN, citing their findings.
More recent insights can be drawn from the experience of children whose education was disrupted in the early 1990s by the Bosnian War -- with the obvious caveat that life during conflict is very different to life during a peacetime pandemic.
Arnesa Buljusmic-Kustura, who was born in Sarajevo, was about four years old when the nearly four-year siege of the city began. She should have been starting kindergarten. Instead, she and her family were left sheltering in a basement with their neighbors.
"The war and genocide in Bosnia was taking place and for us in the city that really meant that we were completely cut off from the rest of the world," said Buljusmic-Kustura, 32, now a writer, researcher working on genocide education, and the deputy director of Remembering Srebrenica UK.
"We had no electricity, no water, really limited access to food and obviously we were subjected to daily bombing and shelling, as well as ongoing sniper attacks that were really targeting civilians and even children. So going to school was really unsafe," she told CNN.
Instead, the adults took it in turns to distract the children from the situation, with a story or by practicing letters, Buljusmic-Kustura said. "We didn't have formal schooling. What we did have was a community that came together and tried to engage us on a very different level."
When peace came, Buljusmic-Kustura was able finally to attend the school five minutes' walk from her home. By that time she was seven-and-a-half years old, and about two years late starting first grade.
In some parts of the city, impromptu classes had been held under cover for mostly older children as the siege went on, she said.
Many, though, were in the same position as Buljusmic-Kustura. "That first day of school I remember not being able to read or write or do those very basic things -- but neither did anyone else," she said.
"Because everybody had sort of experienced the same thing, there was a huge amount of understanding and a lack of this kind of competition that you now see. Because when you come from a place where you have experienced collectively something horrible, [people think] how do we rebuild our lives and how do we move forward?"
Buljusmic-Kustura moved to the United States as a refugee at the