Roll-out of the foundation phase for all under-fives will hit serious problems because funding decisions have been made too late.
That is the verdict of the heads and teaching unions to whom TES Cymru spoke week as Assembly government officials were finally poised to divulge how much cash will be available to local authorities for 2008-9.
There is widespread anger with the government for the delay in coming up with a "simple" breakdown of figures to help infant and primary schools plan ahead for the landmark year in Welsh education.
Every director of education in Wales will know next week how much money they will have to fund the play-led strategy in schools, after a scheduled meeting today.
But it will take even longer for the cash to be filtered through to school budgets, a handicap heads and unions say could jeopardise the scheme's long-term success.
Anna Brychan, director of the National Association of Head Teachers Cymru, said the final figures now appeared likely to arrive too late for schools to be fully prepared for the important first year.
"Members are now very worried that it will not be possible to implement the scheme in time," she said.
Many schools say they have been having to guess how many extra staff they will need as they "plan in the dark". Others say they have held back from making changes for fear of huge predicted funding shortfalls, a consequence of a UK-wide slowdown in the economy.
The foundation phase has proved hugely popular with participating pilot schools. But over the past 12 months cracks have appeared, with many infant and primary schools reporting concerns about their ability to meet the staff-pupil ratio of 1:8 for under-fives.
There are worries that teaching staff will have to be "poached" from special needs to make up the required numbers. Schools are also concerned about finding the money to buy new equipment and ensure safe facilities outdoors, a vital part of the play-led strategy.
Margaret Evitts, head of Gungrog Church in Wales Primary in Powys, said the FP had to be implemented properly or not at all. She already has two students working in her school who could be trained up as teaching assistants.
"At the moment I don't know if I will be able to afford that," she said.
Sue O'Halloran, head of Garth Primary School in Bridgend, said she needed three extra teaching assistants by September.
"I cannot plan anything as we have had no indication of any funding," she added.
UCAC, the Welsh-medium teaching union, is meeting the Association of Directors of Education in Wales separately today to warn that time is running out and schools need to know quickly what their budgets will be.
Gruff Hughes, the union's secretary, said: "When schools face redundancies, heads need to know the budget breakdown."
John Davies, lifelong learning spokesperson for the Welsh Local Government Association and Pembrokeshire council leader, said his local authority had been concerned at the delay.
Nigel Hughes, head of Ysgol Rhiw-Bechan Primary in Powys, a pilot FP school, said he did not currently have enough money to train an extra seven teaching assistants, as well as one higher level TA, to meet required pupil-to- staff ratios.
All fear huge shortfalls in the funding when it is announced, as well as a shortage of trained staff. Strike action has already been threatened by education union the NASUWT if not enough money is found for a raft of new initiatives in 2008-9, including the FP.
Local authority education officers in Powys have predicted the county will receive pound;210,000 for setting up a support grant in 2008-9 and a pound;50,000 training grant each year for the next three years to pay for extra staffing costs.
In a report which went before the council's board in January, it is said that funding indications are "significantly less" than planned for. The FP will be rolled-out across all Welsh schools for three to seven-year-olds by September 2010. A higher staff-pupil ratio of 1:15 is recommended by the government for five to seven- year-olds.
But 2,300 teaching assistants are urgently needed for implementation - 1,300 from this September and 500 each over the following two years.
The government announced it has given an additional extra pound;15 million for the FP in 20089, with an additional pound;48m the following year and pound;33.4m on top of core funding in 201011.
The extra money for early years education was awarded in revised plans that were passed in the Senedd last month.
An Assembly government spokesperson said: "Subject to discussions today, officials will write to directors of education as soon as possible next week. Details of the elements to be funded from the foundation phase revenue grant will be included in the letters. Responsibility for appointing new staff will rest with the schools.
Leader, page 28.