According to Michael Gove, Andreas Schleicher is "the most important man in English education".
As the person responsible for the Programme for International Student Assessment (Pisa) tests, his work has been referred to on countless occasions as justification for the education secretary's breakneck overhaul of the British school system.
But, in an exclusive interview with TES, Mr Schleicher warned that the academies programme risks reducing cooperation between schools and creating a wider gap between the best- and worst-performing schools.
While voicing cautious support for Mr Gove's controversial plans to give heads more control over setting teachers' pay, he also admitted that there was no clear evidence of the benefits of introducing performance-related pay in schools.
As one of the most famous faces in global education, Mr Schleicher, who is deputy director for education at the Organisation for Economic Cooperation and Development, has many different interest groups to keep happy.
He was in London last week to address the conference of Education International, the global federation of education trade unions. The night before, he admitted to delegates, he had met with Mr Gove.
Not surprisingly, then, his view of academies is nuanced. "There are several challenges involved and I don't think there are yet convincing answers to those," he told TES. "How do you encourage effective sharing of ideas?
"How do you get the most talented teachers into the most challenging classrooms; get the best principals into tough situations? Where I think the academy system works positively is that it enables a lot of innovation at the front line, but how do you get it (to spread) into the system?
"I think that is going to be a big challenge. There's also the question whether you can counter the trend towards growing disparities that is inherently linked with such a choice."
Mr Schleicher added that the academies structure had "big promise" but insisted that "a lot of things need to happen to create incentive structures for people to give back and contribute to a system".
Another of Mr Gove's recent reforms was the move to effectively abolish the main pay scale, giving schools the freedom to set teachers' pay based on performance. Mr Schleicher described the approach as "a meaningful way to address the issue (of teacher performance)", which is similar to successful schemes already in use in countries such as Sweden.
"They have different sort of progressions of careers linked to different work responsibilities and different pay," he said. "That's very much the future. That's really what education needs to get to grips with. You still have this industrial work organisation; everyone is equal, everybody gets the same pay. That just doesn't make much sense."
However, Mr Schleicher admitted that the evidence on performance-related pay was "not clear-cut", and warned that principals with "really good human resource management" skills are needed to make it a success.
During the conference, several union leaders raised fears about politicians using Pisa data out of context to support their political reforms, with Mr Gove coming in for particular criticism from Patrick Roach, deputy general secretary of teachers' union the NASUWT, for his "selective" use of Pisa rankings.
Mr Schleicher told TES he shared some of these concerns. "Absolutely, I think the selective use of evidence has been a problem and is a problem," he said. "But today you can statistically account for 85 per cent of performance variation in schools. So your room for making claims that are not backed up by evidence is a lot smaller than it was."
Mr Schleicher also stressed the importance of politicians and union leaders coming together for the international summit on the teaching profession, being held in Amsterdam in March. "The more perspectives we have, the stronger we can build an evidence base and the less room there is for arbitrary political decisions," he said. But on this issue, it seems that Mr Gove does not agree: he has no plans to attend.
Schools should become hubs of cutting-edge research into education in an attempt to speed up innovation, according to Andreas Schleicher, deputy director for education at the Organisation for Economic Co-operation and Development.
"Education is a field where we trust our instinct, where we trust our experience, where we trust our tradition and we don't look at the idea of research in schools," he said.
"That's why the field moves very, very slowly. Research in medicine is not done by some academics in a lab at all, but by practitioners.
"They work at the front line in a hospital to study the efficacy of their own practice. I think that (approach) is totally accessible for education."