Some of the most deprived secondary schools in the country could see their budgets soar by up to pound;1 million due to the pupil premium, the first research has revealed.
It is expected that the pound;2.5 billion supplement, which will hand schools extra cash for every deprived pupil they take on, will be based on the number of children receiving free school meals.
And according to numbers released by Education Data Surveys (EDS), a sister company of The TES, the funding method could see some schools, particularly in inner-city areas, benefit by as much as pound;1 million in additional funding.
In contrast, schools in rural areas with low numbers of pupils receiving free school meals, particularly in the north of England, would receive as little as pound;35,000. This will fail to cover other losses from wider cuts in school funding and could force them to close.
John Howson, managing director of EDS and president of the Liberal Democrat Education Association, said that while some schools would see major benefits from the funding formula, others could go to the wall.
"If it were a fixed fee per pupil on free school meals you could see schools getting close to pound;1 million more," Mr Howson said.
"Small rural schools with low free school meals will not get much extra, and if they have falling pupil rolls and are with a deficit budget they will struggle. If their local authorities couldn't prop them up then they might face closure. Many of these schools would most likely be in Tory MP's constituencies."
These figures may change, however, when details are revealed.
"If it is a top-up to a national fixed amount then schools in well-funded areas would receive less," Mr Howson said. "But even then, if a school of 1,000 has 70 per cent of its pupils on free school meals, it would mean 700 pupils getting pound;1,000 or even pound;500 and this would produce between pound;350,000 to pound;700,000."
The news that schools in the most deprived areas would benefit most was welcomed by David Carter, executive principal overseeing three federated academies in Bristol - Bristol Brunel, Bristol Metropolitan and John Cabot, which cater for some of Bristol's most deprived pupils.
"That schools which educate the largest numbers of disadvantaged students are to be the beneficiaries of the pupil premium is good news for those school leaders who have a moral purpose to bringing equality to educational opportunities."
But schools with low free school meal numbers are unlikely to see benefits.
Councillor John Watson, deputy leader of North Yorkshire County Council and executive member for schools and 16-19 education, said he was aware of the risks.
"It is a concern of ours at a time when we are having to make cutbacks to our overall local authority budget, but we will have to wait and see how it will be allocated," he said.
Graham Stuart, Tory MP for Beverley and Holderness in East Yorkshire and chairman of the Commons education select committee, added: "I would be concerned if this were to lead to additional disadvantage for rural areas that already struggle and do not get a fair share of the national resources."
Martin Freedman, head of pay, conditions and funding for union the Association of Teachers and Lecturers, said: "There will only be a real- terms increase to school spending because of the premium, but not all schools will receive as much with the premium so there may be a reduction."