Is the new head of Ofsted going to come from the United States?

It has been confirmed, although still unofficially, that ministers are seriously looking in that direction for the next education watchdog for England.

Sir Michael Wilshaw's term of office will end this year and the government - it's up to them rather than Ofsted - is casting its recruitment net overseas.

In particular, they are considering candidates who have been involved in the charter school movement, state-funded independent schools, with a similar ideological DNA to academies and free schools in England.

The big impact of charter schools has been in the most deprived urban areas, credited with re-energising schools that had been in a state of chronic decline.

It's a claim rejected by their opponents, particularly in US teachers' unions, who say that the successful glitz and PR around charter schools is not backed up by any significant long-term advantage.

Some charter schools do well, some do badly... like any other type of school, they argue. The current mayor of New York, Bill de Blasio, has been accused by charter school groups of putting up "roadblocks" to their expansion.

Image copyright PA Image caption Sir Michael Wilshaw, who has dominated the education landscape, is standing down this year

But what kind of candidates are likely to emerge?

The names in the frame so far include Dave Levin, co-founder of the Knowledge Is Power Program, which runs more than 180 schools.

But he says he has not been contacted by anyone at the Department for Education and is "not considering any position at Ofsted".

Mr Levin says he is "fully committed to continuing our work at KIPP" in helping to put disadvantaged pupils on the path to college.

Another name is Doug Lemov, who runs Uncommon Schools - and for anyone reading the tea leaves in such things, he tweeted about Arsenal's game after being mentioned by the Sunday Times as a possible candidate for this London-based job.

Eva Moskowitz of Success Academy is also mentioned, a deeply controversial figure in US education, whose school chain is currently firefighting a viral video of a teacher ripping up an infant pupil's homework in front of them.

A much stronger candidate, so far not mentioned, might be Geoffrey Canada, president of the Harlem Children's Zone.

Also suggested by other insiders has been Michelle Rhee, who runs an education reform group and is a former head of state schools in Washington DC.

But there are also informed opinions arguing that the idea of a US watchdog might be a smokescreen and there are a lot of practical complications that might make such a transatlantic transfer unlikely.

For instance, the salary might be a barrier. It has to be enough to tempt someone over - but if it's too much it's going to be a constant source of complaints.

It's categorised as one of those "sounds great on paper" ideas.

Image copyright Getty Images Image caption New York mayor Bill de Blasio has been accused of trying to obstruct new charter schools

And a candidate closer to home might be the frontrunner, such as the national schools commissioner, Sir David Carter.

There are also some big differences between the US and England's school systems. First of all, there is no US school system - it's organised at state and city level, with all the variability in standards and resourcing that come with that.

In terms of international education rankings, the US is a pretty unimpressive performer. In the Pisa tests, run by the OECD, the United States is behind the UK on every measure.

This mediocre average conceals an even more depressingly polarised underlying picture.

Academics at Harvard and Stanford have looked at Pisa results for individual US states, comparing them to other countries. It found that some, such as Massachusetts, have standards that would match most other places in the world.

But there were other states, particularly in the south, which had some of the worst results in the developed world.

Image copyright Getty Images Image caption There are tens of thousands of pupils in charter schools in New York

In individual cities there are also some calamitous problems.

In Detroit, according to the results of US tests, only 4% of 13- to 14-year-olds in the city's state schools are proficient or better at maths. This is a city where teachers have been banned from striking and are closing schools by calling in sick on the same day.

These kind of extremes do not really have a parallel in England.

Another big difference is that much of the talk around charter schools is about rescuing failing schools in places such as New York.

But in England's school system, London is the jewel in the crown, outperforming the more comfortably quilted shires.

The narrative of evangelical educators working in the bleakest urban, violent wastelands doesn't really translate.

An American in Ofsted would be more likely to have to take on the rusting arcades of a rainy seaside town, counting the bookies and pound shops rather than the gang victims.

Image copyright Thinkstock Image caption In post-hurricane New Orleans, many schools became charter schools

National Association of Head Teachers' leader Russell Hobby was not enthused by the idea of a US import, saying that "seeking home-grown talent might be wiser".

"Quality of leadership is usually considered higher in the UK, so there's a good pool to draw from. Our unions are nothing like the US unions in terms of restrictive practices."

And Christine Blower, leader of the National Union of Teachers, said: "If the government is scouring the world for a new head of Ofsted they should look to Finland.

"It is universally agreed to have an excellent education system characterised by co-operation, collaboration and trust. A far cry from the charter school ethos of the US."

There is another major dimension to this story. As well as talking about who gets the job, perhaps the more important question is about how the job is going to be redefined.

Sir Michael Wilshaw is probably the most influential figure in England's education system, with his views and rulings often overshadowing education ministers.

Image copyright Thinkstock Image caption In England, the capital's schools are seen as a strength rather than a weakness

Although he has faced much criticism from the teachers' unions, Sir Michael has been a powerful force in defending a comprehensive school system, rooted in public service and the public sector.

The teachers' unions have long complained about the Ofsted head, but they might come to regret his departure.

The more free-market advocates of academies have resented the regulatory, interventionist force of Ofsted - and they would not be unhappy to see its power being cut down to size.

Ofsted's willingness to take on academy chains has been intended to raise standards, but will also have raised hackles.

When Sir Michael steps down, it will be the chance for ministers to decide how sharp they want the teeth to be on their new watchdog.