By Hannah Richardson
BBC News education reporter
Daily spending on schools in England will be lower by 2022-23 than it was in 2009, according to a report published as pupils are returning to class.
The Institute of Fiscal Studies (IFS) says that by next September, available funds will be down 1-2% on 12 years ago, despite £7bn from the government.
It comes as schools are working hard to help pupils catch up learning lost to the past 18 months of Covid disruption.
The government has said it is expanding its £1bn tutoring catch-up scheme.
And as youngsters across England return to school for pre-term Covid testing, schools will be able to access funds to use a national tutoring scheme or use their own teachers to offer pupils support.
Education secretary Gavin Williamson said he expected a greater sense of normality in schools this term thanks to vaccination programme.
"That extra protection helps us find that sensible balance between protecting staff and students and ensuring education is not disrupted," he said.
"Keeping children in the classroom helps them catch up.
"It has given pupils real, hands-on help to support them following the disruption caused by the pandemic and we want to build on that success. So I'm delighted to be further expanding the National Tutoring Programme," he added.
The government hopes its tutoring programme will support up to six million pupils over the next three years.
Despite plans for regular Covid testing of staff and pupils. there are concerns among head teachers, school staff and scientists about high rates of virus in a largely unvaccinated population.
Scientists have warned that the increased mixing related to reopening schools, combined with reduced health and safety rules, could lead to a rapid raise in cases throughout September.
'Live with the virus'
It is unclear how this might play out in terms of further disruption to education, with anyone testing positive still required to self-isolate for 10 days.
The government insists its decision to lift restrictions maintains the balance between precautions, and allowing schools and young people to get back to normal.
This includes the ending of social distancing, bubble groups and face mask requirements, although twice-weekly Covid testing remains.
The requirement for close contacts of Covid cases to self-isolate, which saw millions of school days lost by pupils, has also been lifted.
But Labour is highlighting how UK schools under tighter restrictions have seen more disruption linked to Covid than all but one of their European counterparts.
It quotes House of Commons Library research showing a 44% disruption rate in the UK between January 2020 and July 2021.
Only Italy had a higher rate at 48%, the figures based on data from the Oxford Covid-19 Government Response Tracker said.
Labour's shadow education secretary, Kate Green, said: "[Education Secretary] Gavin Williamson is again burying his head in the sand, ignoring the advice of scientific experts and risking creating a climate of chaos for schools if Covid rates rise.
"Rather than ignoring reality, the Conservatives should be listening to the pleas of parents, teachers and Labour to get proper ventilation and Covid-secure measures in place to keep children learning together in class."
The IFS funding report analyses the impact of the extra £7bn invested over three years from 2019 on budgets which were already 9% down on 2009 levels.
The independent analysis says this government investment over three years from 2019 has filled, and will continue to fill, much of the budget black hole, but not all of it. This leaves per pupil funding down on 2009.
It also finds that because of recent changes to school funding calculations nationally, secondary schools in more deprived areas lost more like 14% compared to the national average of 9%.
This means there was more of a hole to fill in these schools.
Added to this is the fact that many of these schools will be facing additional Covid pressures because of the increased detrimental impact of the pandemic on disadvantaged pupils.
Josh Hillman, director of education at the Nuffield Foundation which co-funded the report, said: "This IFS research reveals that the largest reductions in per pupil spending have been experienced by schools in deprived areas.
"We also know that the most disadvantaged pupils are more likely to be behind on their learning as a result of disruptions to their education during the Covid crisis."
The IFS report examines trends in day-to-day core school spending in England, and excludes extra spending during the pandemic, such as the one-off £3bn allocated so far for catch-up spending.
A Department for Education spokesman said the government is providing the biggest uplift to school funding in a decade - £14 billion in total over the three years to 2022-23.
"Next year, funding is increasing by 3.2% overall, and by 2.8% per pupil, compared to 2021-22.
"The National Funding Formula continues to distribute this fairly, based on the needs of schools and their pupil cohorts," he added.
National Association of Head Teachers general secretary Paul Whiteman said there was no escaping the fact that the schools have had, and will continue to have, to make cuts to provision until this is properly addressed.
He added that with losses being felt the hardest in disadvantaged areas, the government's levelling up "starts to sound very hollow indeed".