Some 85% of school leaders said they were "unconfident" in the education inspectorate for England, data revealed by the NAHT school leaders' union has revealed.

The survey of 1,890 teachers in September and October saw just a fifth say they felt Ofsted inspection reports provided useful information for parents.

Almost two-thirds (64%) said the one-word grade given by the Ofsted for a school's effectiveness - ranging from "outstanding" to "inadequate" was not reliable.

When asked how they felt about their school's next inspection, the top five words used by leaders included "anxious", "sick", "stressed", "terrified" and "dread".

The survey findings were published on Thursday, just days after a damning inquiry found Ofsted was "not fit for purpose".

The Beyond Ofsted inquiry found Ofsted has a "detrimental impact" perceived by some to be "toxic" - and called for "transformational change".

The inquiry was launched in the wake of the death of headteacher Ruth Perry, whose family say she took her own life after facing the "deeply harmful" pressure of an Ofsted inspection at her school, Caversham Primary in Reading.

She died in January while waiting for the outcome of the assessment, which saw the school downgraded to inadequate.

Two academics called for the Health and Safety Executive (HSE) to investigate every work-related suicide after the tragedy - which is the subject of an inquest due to begin next week.

Ofsted announced changes to improve inspection arrangements and ease pressure on teachers and school leaders in June, in response to Ms Perry's death.

Ofsted is 'broken'

The NAHT survey findings should be a "wake-up call for ministers", general-secretary Paul Whiteman said.

"Far from driving school improvement, inspections are seen as inaccurate, unreliable and of little use to parents or schools.

"Ofsted is clearly no longer fit for purpose, even after the limited changes it was forced to make in the wake of the Ruth Perry tragedy."

The Ofsted grades can be "devastating" and "cannot possibly capture a whole-school performance", Mr Whiteman said.

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Many school leaders with positive inspection results have reported the negative impact of the process on their health, the survey found.

Mr Whiteman said the findings should be the "number one priority" for the new Ofsted chief inspector, academy trust leader Sir Martyn Oliver, who starts in January.

He takes over from Amanda Spielman, who is due to publish her final annual report into the state of education and social care in England during the 2022/23 academic year on Thursday.

It will suggest the social contract between schools and parents is "fractured" since the Covid pandemic - with more than a fifth of pupils in England "persistently absent", particularly on Mondays and Fridays.

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Another report from the Institute for Public Policy Research concluded that "overly simplistic" school inspection judgements can trigger abrupt management changes, fuelling a "football manager culture".

But an Ofsted spokesperson said nine out of ten schools said they believed an inspection will help them improve.

"Children only get one chance at education, and inspection ensures the standards are high for all children," they added.