The debate over the cause of the stunning improvements in London’s state schools reopened today, with new research claiming to show that the success is not just down to the ethnicity of the capital’s pupils.

Analysis by the CfBT Education Trust shows that teenagers in inner London from all major ethnic groups have improved their average GCSE performance at a greater rate than their ethnic counterparts elsewhere in the country.

Tony McAleavy, the charity’s research director, said he was confident this meant that other factors besides ethnicity were behind the improvement.

“Regardless of students’ ethnic background, on average a pupil in inner London performed substantially worse than one elsewhere in the country in 2006, but by 2014 performed substantially better,” he said. “We think that this is linked to improved school effectiveness in the capital. London is setting a global benchmark for learning and success.”

A report published in November by Professor Simon Burgess concludes that results in London secondaries are better than the rest of England simply because they have a higher proportion of ethnic minority pupils.

The report by the Bristol University academic finds that the greater progress between primary school attainment and GCSE results associated with being a London pupil disappears once ethnic background is taken into account. The study suggests a similar situation in Birmingham, which also outperforms the rest of the country and has high percentages of ethnic minority pupils.

These findings are in marked contrast to an earlier CfBT report on London’s state schools, which concludes that ethnicity is not an explanation for the capital’s success.

Now, the charity has softened its stance, saying that “ethnicity is not the only factor in London school success”, although Mr McAleavy went further and told TES he did not think it was the main factor.

However, the CfBT analysis, showing that all ethnic groups do better in London than elsewhere, does not necessarily prove his case. It would be perfectly possible for a relatively small positive London effect on results to co-exist alongside a much bigger ethnic effect - the two are not mutually exclusive.

That is the view of Sam Freedman, research director at Teach First, who has argued that the CfBT has underestimated the significance of the changing ethnic composition of London’s schools.

He told TES that the latest report had not changed his view: “This is a much less sophisticated analysis than Professor Burgess’. It looks at raw results rather than progress, doesn’t properly break out ethnic groups and doesn’t take account of the proportion of different ethnicities in London versus the rest of the country.

“It certainly doesn’t show that ethnicity wasn’t a major factor in the improvement of London secondary schools.”

The CfBT argues that five key interrelated factors were “critical to London’s success”. It cites the London Challenge school improvement scheme, improved performance by some local authorities, the academies programme, Teach First and good leadership.

Its new report also contains analysis of Ofsted reports showing that London schools were less likely to be judged good or better than those in the rest of England in 2002-03, but more likely to be a decade later.

“They seem to show that there has been a significant change in the relative effectiveness of the schools,” Mr McAleavy said. “That has got nothing to do, I think, with the distinctive ethnicity of London.”

Asked whether the change in Ofsted verdicts were not simply a reflection of the better exam and test results, rather than an explanation for them, he said he did not accept that the two were so closely connected.

There is a lot at stake in what becomes the accepted explanation for London’s improved results. The CfBT advises on education in several other countries, including India, the UAE and Saudi Arabia.

Mr McAleavy said: “There is a real appetite and interest in the London story, globally. That is why we have produced this report. We were trying to come up with something of interest to international policymakers.”

Related stories:

Success of London schools explained exclusively by pupil ethnicity, research finds - 12 November 2014

Tristram Hunt: Labour will bring back the London Challenge - 21 September 2014

The London wonderground - 27 June 2014

Primary schools behind boost in London GCSE results - 23 June 2014