The comments, made by an independent financial consultant parachuted in by the NUT Cymru to investigate school funding, came as it was announced that roll-out of the play-led strategy for reception pupils is to be deferred for another year.
Speaking at the union's All Wales meeting last weekend, John Atkins said schools, knowing the foundation phase (FP) pilot settings had been well-funded, waited for the new budget in the belief that it would cover investment in the FP, having spent last year's money in other areas.
But when the funding failed to emerge, heads realised they would not have the means to implement the scheme, based on similar models in Denmark, Germany and New Zealand.
Roll-out of the FP will now take place only in nursery settings this September. But teaching unions and local government representatives warned this week that it could be a wash-out if the cash awarded - pound;107 million - is not doubled.
David Evans, Welsh secretary of the NUT Cymru, said schools had to accept that they were simply not prepared. Serious complaints of underfunding started last November, but schools had to wait until this April to find out about budgets. The roll-out has since been marred by threats of boycotts, saved only by the announcement of a token pound;5m that many say will just scrape the surface.
Also speaking at the All Wales meeting, Jane Hutt, education minister, admitted: "I know we don't have enough money. I'm living, working and sleeping the foundation phase."
Teachers at the conference said too much focus on the strategy could affect key stage 2, with FP pupils moving to a curriculum that was alien to them.