The funding gap between schools with the biggest and smallest proportions of deprived pupils has more than doubled since the turn of the century, a new study shows.

The research by the Institute of Fiscal Studies (IFS) highlights how the increased targeting of school funding to the most disadvantaged pupils predated the Coalition’s pupil premium policy by at least a decade.

In 1999-00, the fifth of primary schools with the highest proportions of disadvantaged pupils had 17 per cent more funding per pupil than the fifth of primaries with the lowest levels of deprivation.

But by 2012-13 this gap had more than doubled to 38 per cent. The corresponding change in the secondary sector rose from 15 to 39 per cent.

The research also found that secondaries with deprived intakes saved more money. In 2012-13 the most deprived ran a surplus of £260 per pupil, compared to £90 per pupil for the least deprived secondaries.

The news follows figures released by the Association of School and College Leaders this week which  showed that schools in the lowest-funded parts of the country will receive about £1.9 million less next year than those in the best-funded areas - enough to pay for 40 extra teachers,

At the extremes, schools in Wokingham - the lowest-funded local authority area in England - will receive £4,158 per pupil, compared to £7,014 for schools in Tower Hamlets, east London.

Malcolm Trobe, the association’s deputy general secretary, told TES that he thought the increased targeting of school funding towards deprivation could have contributed to those disparities.

But he said historical  geographical funding differences were also a factor and that it was hard to know exactly what was happening because the IFS figures were based on averages.

The government needed to do more work on finding out exactly what funding schools required, Mr Trobe added.

“This boils down to the fact that they need to get back to the basics and determine what is needed as baseline funding for a normal school,” he said.

“It is perfectly right that money is targeted towards deprivation. Schools in disadvantaged areas do need more money. But what exactly how much more money they need to close the achievement gap hasn’t been quantified.”

The IFS study also shows that much more of the extra deprivation funding schools received since 2000 has been spent on teaching and non-teaching support staff than actual teachers.

“Some of these changes were intended by policymakers at the time,” the IFS’ Luke Sibieta said. “But it is not clear they ever intended the scale of the change we see in terms of the numbers of teaching assistants or other non-teaching staff.”

His report argues that schools had opted for more support staff because they offer more flexibility.

“Teachers must be employed on relatively inflexible contracts, are difficult to remove if funding was to decline and schools are not easily able to add an extra classroom,” it says. “Other staff can be employed on relatively flexible and temporary contracts.”

It also notes that other research had shown that teaching assistants had a comparatively weak impact on pupil attainment.

But Mr Trobe said: “The situation is improving as schools have more access to evidence showing how to make best use of teaching assistants.”

Schools had also hired non-teaching staff to take on administrative tasks and that change had freed  teachers up to teach, he added.

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Funding cuts are stripping post-16 education ‘to the bone’ - 15 April 2014