The play-led foundation phase is set to emerge as the main winner from the Assembly government's review of education spending, TES Cymru understands.
Leighton Andrews, the education minister, has vowed that the flagship early years policy will be the first to benefit from any extra cash saved as a result of the review.
It comes after concerns were raised by primary school headteachers in Cardiff that a pound;350,000 funding shortfall could threaten the roll-out of the early years scheme in the city.
The heads were unanimous in their backing of a motion expressing "frustration and disappointment" that they have not been given enough cash to hire the necessary number of extra teaching assistants to honour the recommended adult-to-pupil ratios come September.
Many said that meeting the 1:15 ratio for five- to seven-year-olds would mean having to make other teaching staff redundant.
The Conservatives said the row highlights the need to refocus spending to frontline services in the face of shrinking budgets.
Although the situation seems confined to Cardiff, there are wider fears across the country about the sustainability of the foundation phase given the major financial constraints the Assembly government finds itself under.
But Mr Andrews has given assurances that the initiative remains a top priority for the government, and has said privately that it will be the main beneficiary of his highly publicised spending review, which is set to end this month.
In the light of the recent concerns, some are now starting to question whether it is wise to maintain the recommended teacher pupil ratios of 1:8 for three- to five-year-olds and 1:15 for five- to seven-year-olds, which are not statutory.
Dr Philip Dixon, director of the Association of Teachers and Lecturers Cymru, said "fundamental questions" have to be asked about the sustainability of the foundation phase.
"The ratios are important and the government has given undertakings which must be honoured," he said. "But the ratios alone won't deliver success. The key thing is the quality of the staff employed."
However, Anna Brychan, director of heads' union NAHT Cymru, said the ratios are "crucial" for success. "The philosophy requires a considerable level of adult intervention and guidance," she said.
"Adults need to be of a sufficiently high number and quality to direct the children. We have always regretted that the ratios have not been made statutory."
In response to the concerns raised by the Cardiff heads, the Assembly government said it uses a "tried and tested" financial model to calculate the annual budget needed for the foundation phase, and that local authorities are allocated funds based on pupil numbers. It said it expects authorities to make the best use of this funding, with 90 per cent of the money used to employ additional classroom assistants.
Funding for the foundation phase for 201011 was recently boosted by an extra pound;22 million, bringing the total for the next financial year to pound;76 million.
The Assembly government has invested some pound;170 million for the first three years.
Original paper headline: Extra cash pledge for early years as heads raise roll-out fears