School children have lost an estimated 346 million days of face-to-face schooling this year, according to analysis.
The shocking figure amounts to over eight weeks per pupil this year, in addition to an average of 14 weeks of in classroom learning missed last year.
The disruption has disproportionately hit more disadvantaged children, with those on free school meals 30% more likely to have been out of school in the autumn term.
Labour research also found that pupils across the North of England have had, on average, an additional week out of school compared with their Southern peers.
Half a million children will open their GCSE results on Thursday amid concerns that results will show a further widening of inequalities.
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Labour Leader Keir Starmer called on the Tories to match Labour’s £15bn commitment to a school catch-up programme.
He said: “These young people are excited for their futures and every one of them must be allowed to reach their potential.
"Yet the Conservatives are failing to give children the support they need to catch up on lost learning.
"They risk holding back a generation of kids."
Tuesday's bumper set of top A-level results also triggered concern about widening disparities between private school and state school pupils.
Nearly 45% of pupils were awarded an A or A* after formal exams were replaced with teacher-assessed grades for the second year running.
Some 70.1% of independent school students achieved A or above, compared to just 39.3% of comprehensive pupils.
Exams regulator Ofqual also pointed to how the pandemic had deepened inequalities for black pupils, children receiving free school meals, and students from deprived backgrounds between 2019 and 2021.
Labour analysis of Ofqual data found students on free school meals were 28% less likely to receive an A grade than their peers, while black students were 25% less likely to get the top marks than their white counterparts.
Shadow Education Secretary Kate Green said the figures laid bare the "inequality, unfairness and chaos baked into our education system".
Boris Johnson's former catch-up tsar fired off a warning on Wednesday that "growing inequality" in education could be a grim legacy of Covid-19.
Sir Kevan Collins, who quit his post in June after the PM failed to back his ambitious plans, said: "There's a huge risk that one of the legacies of Covid, the education legacy of Covid, could be growing inequality.
"Now, to tackle that and to deal with that, we need a comprehensive and robust long-term plan.
"I don't believe the recovery will happen naturally and I think, if we don't do something tangible about it, we will have growing inequality in our education system."
The Department for Education said the number of top grades has risen for students from all backgrounds and ministers were committed to helping all students achieve the best results.
It comes as unions warned that overhauling the A-level grading system to tackle grade inflation would be "unnecessarily disruptive" and unfair to pupils.
A-levels are currently graded A* to E, whereas GCSEs were changed to offer 9 to 1 marks to tackle grade inflation.
Officials are said to be considering a similar overhaul for A-levels but it is understood that ministers want to see the results of a consultation on plans for next summer's exams, which is due in the autumn.
A Government source told the Mirror: "It's highly likely that it's an idea which will be considered by ministers as soon as you sit down to have a conversation about grade inflation."
Geoff Barton, general secretary of the Association of School and College Leaders, said there were questions over grade distribution for A-levels after two years of Covid chaos.
But he added: "It seems unnecessarily disruptive, however, to undertake an overhaul of the grading system itself to replace it with numbered grades or some other big change.
"A reform of this nature needs both a clear rationale and a lead-in period rather than landing it suddenly on students and teachers who are expecting A-levels to be graded in the fashion with which they are familiar. It would be very unfair and confusing to move the goalposts at this stage."
Labour warned Gavin Williamson against "playing around with the grading system" and urged him to focus on helping children catch up from the massive disruption caused by the pandemic.
Ahead of results day, the Education Secretary said: "Students should feel proud of their achievements and will now be looking forward to taking their next steps.
"I am also hugely grateful to teachers and school leaders for their hard work to ensure students get the grades they deserve and need to progress to the next stage of their lives."
