sudden shock to children’s lives and education, it also exacerbated trends that were already taking place prior to the appearance of Covid-19.

Some groups – including students in schools that faced relatively longer closures, boys, immigrants, and disadvantaged students – fared even worse. And distance learning, where students logged onto screens for class, didn’t seem to do much to stem the tide of learning loss. In the end, they say, these learning losses could translate to earnings losses and could cost this generation of students trillions of dollars.

“The gaps are there, and they are not disappearing,” says Maciej Jakubowski, an education researcher at the University of Warsaw in Poland, who led the study. The findings match those from other studies. Across Europe, for example, children lost the equivalent of one-to-three months’-worth of learning, with some countries such as Poland and Greece seeing three times that level. Even more significant effects were found in countries including Brazil, Mexico, South Africa and the United states, with more ground being lost in maths and science than other subjects. Another major review of 42 studies across 15 different countries over a year and a half of the pandemic estimated that pupils lost a third of a school year’s worth of learning due to the shutdowns.

These deficits also persisted as the pandemic progressed, with no clear catch up even after schools began to reopen, says Bastian Betthäuser, who studies social inequalities at the University of Oxford in the UK and led that review. “We saw that those early learning deficits were very sticky,” says Betthäuser. “That didn’t grow much worse as the pandemic continued, but we didn’t at that point see a clear trend towards recovery.”

The results were also similar for primary and secondary school students. That came as a bit of a surprise, as the researchers thought the deficits would be greater for younger students, who were less likely to be able to learn on their own. Betthäuser says that could be because school closures were longer and more intense for older students – so they ended up being out of school for longer and missing more material.

Since the pandemic, many schools have tried to catch up students through accelerated learning, but with varying success. But Betthäuser says there are glimmers of hope – evidence from the UK and the US shows there has been some recovery to those large learning deficits – but that it hasn’t been complete. “This recovery tends to be faster for kids from more advantaged backgrounds, meaning that the achievement gaps between kids from different socioeconomic backgrounds remain very large, at times even larger than they were before the pandemic,” adds Betthäuser.

The effects of this sort of unfinished learning can linger, manifesting into hard economic costs to society, says Jakubowski.

For some countries, such as Poland, the learning losses translate into a decline in economic growth of 0.35%. An analysis by management consultant McKinsey estimates that unfinished learning by students during the pandemic could see them earn tens of thousands of dollars less over their lifetime than those whose studies were uninterrupted. This could hurt the US economy by $128bn-$188bn (£94.6bn to £139bn) every year once the students of 2020 enter the workforce.

“That’s a huge economic impact,” says Jakubowski.

Jakubowski says that there are targeted interventions that can help to address learning gaps, such as small-group instruction, or tutoring on specific topics, although it is an expensive solution.

The long-term cost to society may go beyond education though. The Covid-19 lockdowns led to concerns about how children’s physical health may have altered during the pandemic. One study in the UK found that obesity among young children aged between 10 and 11 years old increased during the pandemic, and have persisted. This, the researchers estimate, amounts to an additional 56,000 children being obese. This is likely to be due to changes in eating behaviour and physical activity that occurred in many countries during the pandemic and have perhaps continued. In the long term, this could cost UK society an estimated £8.7bn, the researchers say.

But while the pandemic led to a sudden shock to children’s lives and education, it also exacerbated trends that were already taking place prior to the appearance of Covid-19.

Judith Perrigo, an education researcher at the University of California, Los Angeles, had been watching scores in reading and maths slowly decline in the US for years. Perrigo leads a long-term study of kindergarteners that has been going on for 14 years. The study asks their teachers to give a score on each student’s physical health and well-being; social competence; emotional maturity; language and cognitive development; and communication and general knowledge.

But she and her colleagues found that the pandemic led to an even sharper drop in language, cognitive and social competence skills. The study was unique in that the researchers had been collecting the same data for over a decade, allowing them to see the impact of a universal shock like Covid-19 over the population and over time.

“The story is that the Covid pandemic hurt children developmentally,” she says, although she says her study shows the downward trajectory was already underway when it hit.