One in 20 pupils in England were absent because of coronavirus on just one day last week, as the number of pupils off school with a confirmed case doubled in a fortnight.
A record number of teachers and school leaders were also absent on the same day - Thursday, January 20 - according to the latest figures from the Department of Education.
They estimates that 5.1 per cent of all pupils were off school because of Covid on January 20, up from 3.9 per cent two weeks earlier on January 6.
It meant a record for this school year, 415,300 youngsters were off due to covid - of which 321,800 pupils had a confirmed case.
On January 6, approximately 315,000 children were off of due to Covid, as pupils returned from the Christmas break, with 159,000 of those recording a confirmed case.
A record number of teachers and school leaders were absent on January 20, with nine percent not in school, up from 8.6% on January 6, the latest data also shows.
In total, 4.5 per cent were absent for Covid-related reasons, down from 4.9 per cent on January 6.
General secretary of school leaders' union NAHT Paul Whiteman said schools are "still seeing significant levels of disruption due to Covid, with both pupil and staff absence very high".
"Covid absence figures for pupils are the worst they have been this academic year," he added.
Mr Whiteman said schools are "struggling to keep things running", with nearly 10% of their staff off on average.
"But for some this is much higher," he said.
"Our members are repeatedly telling us that they are having to drop everything to find cover and that just keeping things going is a challenge."
He said headteachers are still "very much in the eye of the Covid storm" and that the disruption is causing "huge pressure" for pupils preparing to sit exams.
On Tuesday, the NAHT called on the Government to review the changes made to GCSEs and A levels this year to mitigate disruptions caused by Covid.
Currently, pupils in England will be offered a choice of topics in some GCSE exams, such as English literature, history, ancient history and geography, as well as exam aids next summer to make up for Covid-related disruption.
For subjects where a choice of topics is not provided, advance notice on the focus of exams will be released on February 7 to help with revision.
But the NAHT union said the Government needed to review its plans to make sure exams are fair for this year's GCSE and A level cohort.
"Advance notice information should be published as soon as possible," Sarah Hannafin, the NAHT's senior policy advisor, said.
