Staff training budgets have been cut to a "shocking" extent, according to a leading Wales headteacher.
Brian Lightman, head of St Cyres School in Penarth, said that money given to schools for continuing professional development (CPD) of staff had been slashed over the past 15 years despite reform of the curriculum.
Mr Lightman, who leaves St Cyres in September to become general secretary of the Association of School and College Leaders (ASCL), revealed that when he joined the school in 1995 he was given a CPD budget of pound;55,000 by the Westminster government.
But since devolution in 1999 the funding available has decreased annually and this year he has received just pound;30,000 for the same purpose from the Assembly government's Better Schools Fund (BSF).
"The difference in 15 years is staggering, and that's without even taking inflation into account," Mr Lightman said.
"While our overall budget has almost doubled since I started, our training budget has almost halved.
"When you consider the scale of curriculum and pedagogical change that has taken place and the level of expertise and competence now expected of teachers, it's even more shocking."
The situation at St Cyres illustrated the financial difficulties faced by heads across Wales, who were increasingly frustrated at being expected to achieve more with fewer resources, Mr Lightman said.
The Assembly government has reduced the cash available to schools through the BSF by a third and axed the annual pound;3 million cash pot for CPD from the General Teaching Council for Wales (GTCW).
Mr Lightman said: "If we can't train our workforce to the standards we need, we can't make schools as successful as we aspire to."
David Reynolds, professor of education at Plymouth University, said the situation at St Cyres was indicative of the Assembly government's "poor" education spending record since devolution.
Research carried out by Professor Reynolds for TES Cymru in 2008 revealed a pound;496-per-pupil spending gap with England, which has since grown to pound;527.
Professor Reynolds said: "Countries with highly successful education systems place a high priority on in-service training expenditure, and the fact that we are squeezing the money available is very worrying indeed."
An Assembly government spokeswoman said: "We have had to make difficult choices about our financial priorities due to the economic climate and this has required us to end the individually focused CPD programme administered by the GTCW. We are considering the best way to develop and support teachers and school leaders in more effective ways."