About 2 million children in the UK have done barely any schoolwork at home during the coronavirus lockdown, a study suggests.
Around one in five pupils have carried out no schoolwork at home, or less than an hour a day, since schools closed partially in March, research by UCL Institute of Education (IOE) shows.
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Researchers estimate that this equates to approximately 2.3 million children across the UK.
The study suggests that only 17 per cent of children put in more than four hours of schoolwork a day.
The findings come as ministers face pressure to get children back to school as soon as possible.
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Last week, education secretary Gavin Williamson was forced to admit defeat over plans for all primary schools to reopen fully before the summer holidays.
The research, carried out at in April, suggests that children locked down at home in the UK spent an average of 2.5 hours each day doing schoolwork.
The figure is around half that suggested by previous research, which implies that "learning losses are much greater than feared", according to the study.
Children who are eligible for free school meals (FSM) appear to have been additionally disadvantaged during lockdown.
Only 11 per cent of children in receipt of FSMs spent more than four hours a day on schoolwork, compared with nearly a fifth (19 per cent) of pupils who are not eligible for free school meals.
Nearly a third (31 per cent) of private schools provided four or more online lessons daily, compared with just 6 per cent of state schools.
The study was based on a survey of 4,559 households in the UK during the last two weeks of April.
It found that the amount of offline schoolwork was lowest in North East England, where the proportion of pupils receiving four or more daily pieces of work was 9 per cent, compared with the UK average of 20 per cent.
Professor Francis Green, the lead author of the study, said the findings paint a "gloomy picture" of missed schooling and low take-up of academic work at home.
He said: "The closure of schools, and their only partial reopening, constitute a potential threat to the educational development of a generation of children.
"Everyone is losing out in this generation, some much more than others. Better home schoolwork provision, and better still an early safe return to school for as many as possible, should now become a top priority for government."
The research also suggests that one in five children on FSM had no access to a computer at home, compared with 7 per cent of other children.
"The lack of a computer is likely to considerably harm their ability to do schoolwork at home, submit it and have it checked," Professor Green added.
The publication of the research comes as politicians, education leaders and charity heads call for children eligible for FSM to have internet access at home.
In an open letter, more than 40 senior figures, including former education secretaries, have called on the government to provide internet access to 1.3 million disadvantaged pupils.