Government funds earmarked for primary schools' Covid recovery efforts will be "entirely wiped out" by a change in the way pupil premium funding is allocated this year, headteachers have warned.
The Department for Education announced last month that the average primary school will receive £6,000 in government funding as part of its Covid "recovery premium" to "further support pupils who need it most".
But the NAHT school leaders' union has found that this cash will be offset by losses incurred as a result of a change in the way pupil premium funds are assigned this year.
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Announced quietly before Christmas, the policy shift means that the government will calculate the number of children attracting pupil premium funding from April based on a census from last October, and not in January, as schools had been expecting.
This means children who became eligible for free school meals between October and January will now not attract pupil premium money in school budgets allocated from April this year.
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Tes reported earlier this month that a group of five local authorities across London estimated a total shortfall of more than £3.5 million as a result of the change.
The NAHT has now done a survey of its members to assess the extent of the damage to school budgets.
It reveals that almost two-thirds of primary schools will be left worse off due to the change, even after the recovery funds are taken into account.
The union asked its school members: "How many pupils in your school became eligible for pupil premium between the October and January census, and will therefore not receive pupil premium for 2021?"
In response, 62 per cent of school leaders said five or more of their pupils became eligible for the funding during that time.
Currently, primary schools receive £1,345 for children entitled to the pupil premium, or £2,345 for looked-after children.
The NAHT found that lost funding for five pupils at the lower rate would, therefore, equate to £6,725 – more than the £6,000 allocated to the average primary as part of the government's "recovery premium".
A third of school leaders (33 per cent) told the NAHT that 10 or more of their pupils became eligible for the funding between October and January.
For these schools, Tes calculated that the change would result in lost funding of at least £13,450.
And 10 per cent of school leaders reported that at least 20 additional pupils became eligible during that time – equating to a funding gap of £26,900 or more.
Paul Whiteman, NAHT general secretary, said the government was "giving with one hand while knowingly taking away with the other".
"A three-month gap may not seem like it would make a big difference but, given the volatile financial situation for many families due to Covid-19, it is an exceptionally bad time to implement this change," he said.
"A significant number of children appear to have become eligible for help via pupil premium during that time and these children will now not receive any additional funding for another whole year.
"Worse, the children who are losing out are exactly those children most in need of additional support as they return to school."
Mr Whiteman claimed that the government had failed to heed his union's warnings over the impact of the change.
"The government may say 'no child left behind', but with this simple 'administrative tidy-up', they have found a way to snatch back funding from schools and to further entrench educational disadvantage for the poorest families," he said.
"We warned them that this could be the unintentional consequence of making this change during the pandemic, and we have raised our members' concerns about the situation they now find themselves in repeatedly. But our warnings have fallen on deaf ears.
"In stark contrast to their promises to put children and young people at the heart of the pandemic recovery, the reality is that the government is taking funding away from schools, leaving them worse off at a time when they need every possible resource available to them to help the children that most need it."
He added: "The government must put this right. We aren't asking for additional money here. Only for what schools would have received if this census date change hadn't been implemented. If they don't they will be abandoning those children most in need at the most critical time."
The findings are being presented at the NAHT's school leaders' summit today.
A DfE spokesperson said: "We moved to using the October census to calculate pupil premium allocation so that schools know their budget earlier in the year, helping them to plan ahead. We expect pupil premium funding to increase to more than £2.5 billion in 2021-22, reflecting an increase in the number of eligible pupils.
"We are taking steps to make sure every pupil gets an excellent education, no matter their background. That's why we continue to allocate pupil premium funding to schools at unchanged per-pupil rates, in addition to the significant new catch-up and recovery funding we have introduced, which is targeted towards schools most in need to support disadvantaged students' attainment."