Why, 15 months after pupils and teachers submitted allegations of widespread cheating at a Dulwich academy school, have exam boards failed to conclude their inquiries?

Please wait while this video loads. If it doesn't load after a few seconds you may need to have Adobe Flash installed.

As a mum of school-age children in south London, I'd heard fantastic things about Kingsdale Foundation School in Dulwich. So, it seems, had the prime minister, who visited last year and described it as "brilliant". Ofsted rate it "outstanding". Which is quite amazing when you consider that a decade ago it was a sink inner-city comprehensive.

But a cloud now hangs over the school which is proving hugely damaging for staff, pupils, prospective pupils and the wider community.

We've been passed numerous allegations from both teachers and pupils describing blatant, systematic cheating. The allegations cover six academic subjects and 10 different qualifications. All in all, nearly two dozen pupils and teachers have sent statements to the exam boards blowing the whistle on the school.

One pupil, Chloe Smith, who took her GCSEs there in 2011, told me teachers who weren't even supposed to be in the room went round telling pupils the answers.

Extra marks

"He started pointing out my wrong answers and telling me to correct them and then started showing me how to get extra marks on the ones which were already right," she said.

A former teacher, who didn't want to be identified, said that Kingsdale "moderated" coursework marks, so that some pupils who had got a D grade got a B instead. "Numbers were being plucked out of the sky," she claimed.

Numbers were being plucked out of the sky. Former teacher, Kingsdale Foundation School

But what's as disturbing is the apparent failings of the investigation the whistleblowers triggered. They sent a dossier of evidence to the exam boards concerned, but 15 months on, the inquiry is still ongoing.

Pupils who submitted evidence haven't even been interviewed, and as worryingly, teachers who turned whistleblowers say the exam boards could have done more to protect their anonymity.

'Detrimental effect'

Since starting researching this story in July, we've also established that the boards' investigation won't ever be published. Local MP and former minister Tessa Jowell, said she's "enormously concerned" that the instability is having a "detrimental effect" on children being taught at Kingsdale now.

She told me there are wider concerns about a lack of coherence in the way schools are regulated, particularly as the burgeoning number of academies aren't overseen by authorities.

This really reveals something profoundly disturbing about the new academy status. Tessa Jowell MP

"I think this really reveals something profoundly disturbing about the new academy status. I took the responsibility to the then minister for education because I was so concerned about the turbulence in the school, the instability... and the minister as he was then, Nick Gibb, basically said there was absolutely nothing he could do about it because of the independent status of Kingsdale as an academy. And that is completely unacceptable," she said.

The school believes the allegations are unfounded and that its name will be cleared.

Government favourite

In a statement, it said: "We are satisfied that the investigation to date has not highlighted any evidence of institutional examination malpractice at the school. The welfare of students at Kingsdale remains the school's top priority and we remain confident in the examination processes at the school."

This is just one school - albeit a government favourite. But if after 15 months the exam boards have failed to conclude their inquiry or publish their findings, there are worrying questions about how similar complaints are investigated up and down the country. And how much faith pupils and parents can have in the results their local schools are reporting.

More on this story