The government’s ex-academies tsar has cast doubt over schools that claim they have turned themselves around in less than a year.

Sir David Carter, who was national schools commissioner until this summer, today called for a “really intelligent, grown-up conversation” about how long school improvement really takes.

Speaking at the Global Teacher Development Forum at Chobham Academy in East London, he said: “One of the things that we have got to be better at in this country is having a really intelligent, grown-up conversation about how long real school improvement takes - that it’s not a quick fix, it’s not linear, it’s not formulaic.

“Any school that tells me they are turning themselves around in six months, and they have gone from special measures to good in less than an academic year, either the inspection judgement was wrong or you’re not being truthful to yourself.

“That kind of deep improvement and change over time takes three to five years, in my experience of having schools that were in deep trouble in my trust and schools that I have seen as a commissioner.”

‘Look after teachers’ wellbeing’

Sir David also warned that school leaders who fail to treat their teachers as human beings as well as professionals will not get the best out of their workforce.

He spoke as a new survey showed that 31 per cent of teachers have experienced a mental health problem in the past academic year

Sir David told the conference: “The leaders who I’ve seen take responsibility for ensuring that teaching is as good as it possibly can be also recognise that teachers need to grow as people as well as professionals.

“The best schools plan for the wellbeing of their staff as well as their professional capability.”

He said that these schools understand that their teachers are also sons, daughters, parents or siblings with a support network of friends.

He added: “But when something happens to that support network, whether it’s a crisis, a challenge, a setback or something joyous, the teacher who arrives in their classroom at 7.30am may feel a very different person to the one who left the afternoon before, so the responsibility of leaders to support great teaching here is paramount.

“A leadership team that doesn’t see its teachers as people leading real lives won’t get the full benefit of that talented workforce being committed to improving the life chances of children.”