Children are losing out on their funding entitlement because schools are holding too much money in reserve, claims a teachers' union.
Schools in England held surpluses of L2bn at the end of the last school year show annual figures, an increase of almost 15% on the previous year.
The National Association of Schoolmasters Union of Women Teachers (NASUWT) says this is "unacceptable".
The government has warned schools against holding excessive surpluses.
Chris Keates, NASUWT general secretary, said that the amount held by some schools was "scandalous".
'Deprivation'
While schools are expected to keep a small reserve for unexpected spending requirements, anything above 5% of annual income for secondary schools and 8% for primaries is considered an "excessive" surplus.
Annual figures show that 38% of England's schools fell into this category, holding L592m in excess surpluses.
"The government believes that the national total of revenue balances and in particular the level of surplus held by some individual schools is too high," said Schools Minister Jim Knight.
There has already been a threat to claw back some of this excess if it has not been lowered by 2010-11 - though ministers dropped plans to act sooner.
Ms Keates said the holding back of money represented "the deprivation of youngsters of their full, in-year, per capita entitlements".
"The point which is missed consistently by those who seek to defend the stockpiling of public money is that these funds are allocated each year to be spent on the pupils, not on either saving for a rainy day or to fund some state-of-the-art building project," she said.