According to Michael Gove, "the most important man in English education" is Andreas Schleicher.
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 Westminster education secretary's breakneck overhaul of the English 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.
Mr Schleicher, who is deputy director for education at the Organisation for Economic Cooperation and Development, was in London this month to address the conference of Education International, the global federation of education trade unions. The night before, he admitted to delegates, he had met 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 sorts 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.
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 Cooperation 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 frontline in a hospital to study the efficacy of their own practice. I think that (approach) is totally accessible for education."