The spending gap between pupils in England and Wales has exceeded pound;500 for the first time, according to new figures.
Assembly government statistics released this week show that each Welsh pupil had pound;532 less spent on their education last year than their counterparts across the border - a difference of 10.1 per cent.
In 19992000 the gap between England and Wales was just pound;58 per pupil - a 2 per cent difference.
The figures match predictions made in TES Cymru earlier this month by David Reynolds, professor of education at Plymouth University, who said the growing scale of the divide will make any attempts to close the funding gap "a very difficult task".
First Minister Carwyn Jones has promised to increase education funding by 1 per cent above the block grant from Westminster from 2011, but teaching unions and opposition politicians said that pledge must now be brought forward in light of the new figures.
When the 200809 funding statistics were first released a year ago, the gap between the two countries stood at pound;496 per pupil, or 9.6 per cent. But when this was revised at the end of the financial year, the gap was found to be pound;532 as the Westminster government had pumped extra funds into England's education system over the course of the year.
According to the statistics, the gap for 200910 will fall to pound;527 per pupil, or 9.7 per cent, but Professor Reynolds said the real figure will actually be much higher when the numbers are revised.
"We are likely to see a difference of more than 10.5 per cent, or pound;550 per pupil," he said. "It reflects the fact that over the course of every financial year England finds more money to spend on education than we do.
"Unfortunately, the earliest the government will start to do anything about this is 2011, when the gap will be substantially wider."
Teaching unions and opposition politicians reacted angrily to the new figures and vowed to put more pressure on the First Minister to fulfil his commitment sooner.
David Evans, secretary of the teaching union the NUT Cymru, said "drastic action" was needed by the government. "This gap causes us real concern and will cause difficulties for schools now and in future. The government must act now before things get any worse."
Philip Dixon, director of the Association of Teachers and Lecturers Cymru, said the situation had reached "crisis point".
"This gap is scandalous - no other word will do," he said. "ATL believes there should be a spending gap between England and Wales - Wales should be spending more than England to tackle the effects of poverty and deprivation."
Conservative shadow education minister Paul Davies said an "unacceptable barrier" had been broken.
"Unless we close this gap, children in Wales will continue to be denied the same sort of learning opportunities enjoyed by pupils across the border," he said.
But an Assembly government spokesman said steps were being taken to address the issue, including the First Minister's spending pledge and the recently announced independent review of how education funding is allocated.
The spokesman added: "In Wales, spending on education has never been higher, having increased by 71 per cent since 19992000, but we recognise the importance of getting more education funding to the front lines."