Standing in front of India's Taj Mahal, tour guide Raju Usmani fears for his daughter's future. With Covid-19 decimating his income, he may have to pull her out of school just as she is catching up after nearly two years stuck at home.
Areeba, 10, is among 1.6 billion children globally - more than 90 percent of all school students - who have been affected by pandemic school closures, which threaten to widen wealth inequalities both within and between countries.
"We're running the risk of a lost generation," U.N. education expert Robert Jenkins told the Thomson Reuters Foundation. "It's a now-or-never moment to turn things around."
Without urgent action, many countries could end up without the skilled workers they need for their future development, said Jenkins, head of education at U.N. children's agency UNICEF.
He is also increasingly concerned about the risk of social instability in countries where a large number of youths are left without skills, jobs or hope.
Children in low- and middle-income nations have been disproportionately affected as their schools tended to shut for longer and they were less able to access remote learning, UNICEF said ahead of the pandemic's two-year anniversary on Friday.
There are no global figures on the numbers who have dropped out. But evidence from Uganda - where schools reopened in January after being shut for a record 22 months - suggests up to 30 percent of children may not return to class.
School closures have increased child labor, adolescent pregnancies and early marriages, children's rights activists say. And many parents impoverished by lockdowns can no longer afford to send their children to school.
The World Bank says classroom shutdowns could cost children $17 trillion in lifetime earnings - the equivalent of 14 percent of today's global gross domestic product (GDP) - as education losses limit their future opportunities.
Critical moment
Educators say the world is at a crossroads. Reopening classrooms is not enough - schools must assess children and adapt curriculums to help them catch up.
Evidence from past crises such as the 2005 Pakistan earthquake show learning losses may even grow after children return to school if teaching does not adjust to meet their needs.
In India, Usmani's problems are far from over. His earnings have fallen to about $5 a day from $13 pre-pandemic.
His wife is sick and his children have fallen way behind as they do not have internet access for online learning.
Areeba, who wants to become a teacher, finally returned to school in January, rejoining the same grade she was in two years ago. She has forgotten sums she used to whizz through.
Her brother Ayazuddin, 5, is back in kindergarten, struggling to remember his English and Hindi alphabets.
It is a common problem worldwide, with some teachers saying children have not only forgotten what they have learnt, but how to learn.
"My children's future depends on the education they get right now," said Usmani, 38, who pays about $20 a month for private schooling because he says the state system is poor.
"I don't want them to get a half-baked education like I did."
Areeba is thrilled to be back in school and rushes home after class to show her father the teachers' stars in her exercise book.
"She really missed school," he said. "Gone are the days when children dreaded going to school. Corona has changed that for sure."
Holistic approach
Education was in crisis even before the pandemic, with 53 percent of 10-year olds in low- and middle-income countries unable to read a simple story, the World Bank says, warning this could now soar to 70%, with potential consequences lasting decades.
But children have not only missed learning. They have also lost opportunities to develop social skills with friends, play sport and, for some, escape troubled homes beset by abuse.
Many have struggled with feelings of isolation, and an estimated 5.2 million are grieving the loss of a parent or carer from Covid-19.
UNICEF's Jenkins said schools must take a holistic approach as they welcome children back, addressing their mental, psychosocial and physical wellbeing.
In many countries, girls have been disproportionately impacted. They often have less access to technology than their brothers, and are more likely to have to help with domestic chores when classrooms shut.
Parents may also prioritize sending a son back to school over a daughter if money is tight.
But for hundreds of thousands of girls there is another barrier to resuming lessons – they have become pregnant.
In 2020, aid agency World Vision estimated 1 million girls across sub-Saharan Africa may drop out because of pregnancies.
Rwanda and Sierra Leone have received praise for measures to reintegrate young mothers back into schools. But stigma, poverty and lack of childcare could still conspire to keep many out of class.
Future impact
Educators say governments must do far more to assess the numbers who have left school, and address obstacles preventing their return.
Many children have quit to earn money. Globally, 9 million risk being pushed into child labor by the end of 2022 because of the pandemic, according to UNICEF.
In the Ugandan capital, Kampala, Kareem Kato, a top science student with ambitions to become an engineer, was about to start secondary school when the pandemic struck.
But the lockdown hit his parents' finances, scuppering his dreams. At 14, he started work as a carpenter to help support his siblings.
His twin sister, Sumaya, hoped to become a lawyer so she could fight social injustice, but was also forced to drop out and now helps her mother on her market stall.
"My schoolmates have nicknamed me 'omuyiribi' which means hustler," said Kareem, holding back tears as he stuffed cushions for a couch. "Sometimes I cry when I watch them returning from school happy, and I'm sweating in the workshop."
Even before the pandemic, Uganda lacked the skilled workforce it needs, analysts said.
"We may not see the impacts right now, but we're going to see it in the future," said Muhire Francis, an economist at Makerere University Business School.
"Two years of school closure is really huge. The impact is going to be long-term and massive."