A headteacher claimed this week she is pound;23,000 short of being able to deliver the play-led foundation phase effectively for under-fives during 2008-9.
Sue O'Halloran, head of Garth Primary School in Bridgend, says she will need three new teaching assistants to meet the recommended staff-pupil ratio of 1:8.
Her local authority has told her she will get only pound;35,000, way down on the pound;58,000 she claims it will cost. "Delivering the FP in my school at the 1:8 ratio is now virtually impossible," she said.
Bridgend county borough council has been given just under pound;1.2 million by the Assembly government for new staff and training in 2008-9. Every LA in Wales is now aware of how much funding they can give schools for new staff.
According to the National Association of Head Teachers Cymru, one-third of them say they will be short by pound;800,000.
The union also says some pilot schools have been told of "dramatic reductions" in their levels of funding on the scheme's roll-out.
Teaching unions have predicted huge shortfalls for months. They now say it is "too little too late".
Chris Jones, Cardiff council's chief schools and lifelong learning officer, said: "Three months ago, the council wrote to the Assembly indicating the money proposed for the initiative was inadequate."
Anna Brychan, NAHT Cymru director, said: "Members argue that the FP's success will be down to maintaining staffing levels."
A government spokesperson said this week that meeting the ratio should remain a top priority.
But Philip Dixon, director of the Association of Teaches and Lecturers Cymru, claimed the government would hide behind the ratio not being statutory when schools were unable to fulfill recommended staffing levels.
"I was amazed the Assembly is now claiming the ratios are not statutory," he said. "They may not be a requirement but they are practically and morally vital."
For 20089 foundation phase "practitioner support and training" from the Assembly government
Isle of Anglesey: pound;597,500
Neath Port Talbot: pound;1,147,500
Vale of Glamorgan: pound;1,065,000
Rhondda Cynon Taf: pound;2,040,000
Merthyr Tydfil: pound;497,500
Blaenau Gwent: pound;587,500