An international expert described by Michael Gove as "the most important man in world education" has publicly contradicted a central pillar of the education secretary's schools policy.
German mathematician Andreas Schleicher was praised by Mr Gove this year for overseeing the Organisation for Economic Co-operation and Development's Pisa (Programme for International Student Assessment) study (see box).
But the men have drawn widely differing conclusions from the evidence on school performance in the world's most advanced economies.
The Government's Importance of Teaching white paper used Pisa findings to back its case that improving the quality of teachers should be at the heart of education reform.
This includes a new minimum requirement of a 2:2 degree for new entrants.
"Top-performing countries consistently recruit their teachers from the top third of graduates," the white paper, published last year, notes.
But Mr Schleicher disagrees: "The frequently cited claim that the best-performing education systems all recruit their teachers from the top-third of graduates ... is not supported by evidence," the German writes in a report for a summit on teachers that Mr Gove attended in New York last month.
The white paper bases its claim on a report last year by consultancy firm McKinsey, which also cites Pisa evidence.
But Mr Schleicher argues for more money to be spent on training existing teachers.
"Successful reform cannot wait for a new generation of teachers," his report says.
"It requires investment in the present teacher workforce, providing quality professional development, adequate career structures and diversification, and enlisting the commitment of teachers to reform."
John Bangs, a member of the OECD's trade union advisory committee who also attended the New York summit, said: "Given Michael Gove's commitment to international evidence and the OECD, the very first thing he should do is to drop the idea that recruiting top graduates is the right strategy."
The Government's white paper does pledge to "develop sustainable approaches to teacher development" and to ensure that teachers have "support" for on-the-job training.
But funding for teachers to take postgraduate degrees is being cut. And Mr Bangs said that by giving money for training straight to schools, ministers were failing to meet their white paper promises.
"The Government is fundamentally not investing in continuous professional development," he said.
"It is running away from the fact that there is an enormous variation in the proportion of school budgets spent on it.
"It is now entirely in the hands of headteachers, who may or may not understand the importance of professional development."
A Department for Education spokesman said: "We agree with Andreas - world-class systems have not just tough recruitment, but rigorous ongoing training throughout teachers' careers.
"That is why we are creating a new national network of Teaching Schools and making sure outstanding staff and schools lead professional development."