Fed-up heads in Norfolk and Suffolk have billed the government for £316m, in a bid to highlight the cash shortfall the region's schools face.
Headteacher associations from 32 counties have urged the government to make school funding across the country fairer as part of the Worth Less? campaign.
All 32 have written to chancellor of the exchequer Philip Hammond – and sent in their own invoices - to highlight the geographic disparities, which they say results in a 'chronic lack of funding to support reasonable teacher/pupil ratios, excellent curricular provision and adequate help for our most vulnerable pupils'.
Schools are funded through a per-pupil sum given to local authorities - but it has historically varied widely, and rural areas have traditionally been left behind.
In the letter, the group says if Norfolk's per-pupil figure matched that in Westminster, Norfolk schools would be £157m better off and Suffolk's would be £159m – reaching the invoice total of £316m.
And, if compared to the figure in Hackney, schools in Norfolk alone would be almost £250m better off - but the government says the calculations are 'thoroughly misleading'.
Carol Dallas, head at Taverham High and one of the four co-chairs of Educate Norfolk, the primary and secondary headteacher associations, said: 'Every child in Norfolk deserves to have the same opportunities as anywhere else in the country. We are not saying that London should receive less money - they need the funding. But so do we.'
In the current school year, government figures show Norfolk was allotted £4,499 per pupil, and Suffolk was given £4,378. In Westminster, the figure was £6,003 and in Hackney it reached £6,847.
When multiplying that by the number of pupils in Norfolk, 119,959, the total amount the county would receive rises from £540m to £821m.
Ms Dallas said it risked pupils being taught in bigger classes and losing out on both support and opportunities.
'In London, there are opportunities right on schools' doorsteps,' she said. 'They are able to build aspiration in school easily because they are right on the doorstep of industry and businesses.
'If we want to take our children to Westminster, for example, to look at becoming a politician, for us that is a much higher cost, but we are funded much less.'
The government is introducing a new national funding formula (NFF) to address the balance, but the letter - which, along with Ms Dallas, is signed by heads Simon Fox, of Flegg High, Penny Sheppard, of Queen's Hill Primary in Costessey, and Sarah Shirras, of St William's Primary in Thorpe St Andrew - says many schools will still receive half of the money that identically sized ones in London will.
Louise Spall, headteacher at Somerleyton Primary School and a representative for Suffolk Primary Headteachers' Association, said it had reached 'breaking point' for many schools.
She said: 'It just seems odd that we aren't funded the same - there's no real reason, and it's just always been that way.
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'Being in a rural area, with the costs of getting children to school and getting out for trips and so on, there's an argument that we should be funded more. It's certainly not easy being part of a rural school community.'
The letter points to the significant impact funding can have on social mobility.
Westminster and Hackney are in the top 10 local authorities for best social mobility - a measure of how someone improves their life chances - while Norwich ranked second from last.
But a Department for Education (DfE) spokesperson said: 'The campaign's calculations are thoroughly misleading, and ignore the fact that under our national funding formula, funding is based on the needs and characteristics of each individual school.
'There are no cuts in funding. Every school will see an increase in funding through the formula from this year, and in 2019/20 all secondary schools will attract at least £4,800 per pupil, and all primary schools will attract at least £3,500 per pupil.'
But in the letter, the heads say they are 'fed-up' of being told there is more money in education, 'when the parallel rising costs are completely ignored, or when the half a million extra children who have swelled our school rolls since 2010 seem to be entirely overlooked'.
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