More than pound;7 million is being wasted by the Assembly government on training secondary teachers who end up working elsewhere in Britain.
The claim by Kirsty Williams, the Welsh Liberal Democrat education spokesperson, came as the government's own updated school census records reveal there was fierce competition for teaching jobs last year, with hundreds sometimes in the running for posts.
Ms Williams criticised the government for continuing to waste money training teachers while Welsh education had funding shortages.
She also accused the government of failing to act on the advice of Oxford academic John Furlong to make a drastic reduction in trainee numbers by 2010, a major recommendation of his 2006 report.
But the government rejected the claim this week, saying it had cut trainee numbers in Wales since 2004-5 and was working towards Professor Furlong's advice to halve the number of trainee primary teachers, and those in secondaries by a quarter.
A spokesperson also said the Welsh Lib Dems' Pounds 7.5 million figure was based on flawed interpretations of statistics sourced from the Higher Education Statistics Agency and the Destination of Leavers from Education Survey.
Based on their research, the Lib Dems say only 41 per cent of 960 teachers trained in Wales went on to teach there in 2006-7.
In 2007-9, the party said 22 per cent of Wales-based trainees went on to teach in other parts of Britain and 11 per cent could not find a teaching post.
"It beggars belief that the Welsh Assembly government has flushed Pounds 7.5m down the pan at a time when the education sector in Wales is seeing huge funding shortages, starting at the play-led foundation phase for under- sevens," said Ms Williams.
More than 8,500 teachers competed for just over 730 secondary vacancies in Wales last year.
The figures, which exclude Welsh-medium schools, were obtained from the government's recently published school census records for 2007.
The fierce competition shows how hard it is for newly qualified teachers to find employment in Wales across the board, particularly in primaries. NQTs applying for advertised posts at key stage 1 had an average one-in-32 chance of being successful last year.
But the competition for teaching posts is not unique to Wales. TES Cymru's sister paper in Scotland, The TESS, last week reported how job prospects for NQTs were becoming "disheartening".
Hundreds of teachers have also been competing for vacancies, with many recruits forced to leave Scotland. Maureen Watt, minister for schools and skills, said it was not in Scotland's best interests to train teachers to see them sit at home or leave the profession.
The brain drain from Wales to England, with many newcomers lured by good teaching packages over the border, has been well documented. More new teachers are also being forced into the supply teaching market.
Assembly minister Jane Hutt told TES Cymru it was important to get the balance right. "I have backed the initial teacher training programme, which will mean there will be a reduction in the training of primary school teachers by up to 50 per cent, and secondary teachers by up to 25 per cent," she said. "The other thing we are doing is introducing the teacher planning and supply plan, another word for a workforce development plan.
"We are working with local authorities to ensure we do support NQTs and we don't train too many of them."
Last year, there were 19,935 applications for 1,520 advertised teaching jobs in Wales.
The greatest competition in any subject at English-medium secondaries was PE, followed by biology, geography and art. In art, for example, 457 applicants applied for 36 posts - less than a one in 13 chance.
But the figures also show there is a much greater chance of securing employment at Welsh-medium schools, with an average of four applicants per post last year.
In his report, Professor Furlong also wanted training providers to be reduced from seven to three in Wales.
His review group took into account pupil population changes in Wales at a national and regional level, teacher retirements and turnover, newly qualified teachers doing supply teaching, cross-border transfers, and "a significant margin of error" when working out the proposed reduction in trainee numbers.
But his recommendations were criticised by some teaching unions that claimed it would lead to job losses, and would "dumb down" the profession.