England's education watchdog was called 'broken' and 'fallible' during the annual Association of Teachers and Lectures (ATL) conference in Manchester. One speaker described Ofsted as 'no longer just disliked, now disdained'.
ATL delegates claim that the results of an Ofsted inspection often depend upon which team of inspectors turn up and the time of year when the visit takes place.
They say pressure from Ofsted forces headteachers to strive for unachievable perfection, putting staff under unbearable strain.
Simon Clarkson, a teacher from Leicestershire, spoke about the negative impact that he claims 'broken' Ofsted inspections have on staff at his school.
"Because they are so subjective, because they are so fallible and because your job, the school's future and your leadership team's future depends on what they say, our headteachers now routinely demand the impossible," he said.
"I am a middle leader. I am told to ask for more and more from staff who are exhausted and have less and less to give. I see solid, dependable colleagues who I know are excellent teachers in tears.
"We need to stop the madness. We need to stop the Alice in Wonderland management of our schools and we need to fix the distorted looking glass that is Ofsted, that is distorting the very way we teach.
"Ofsted is broken, it needs fixing."
The ATL unanimously backed a motion calling for greater scrutiny of Ofsted inspectors, to ensure consistent results across the country.
The union has also published a survey today, which found that 55 per cent of school and college staff say that work pressures are having a detrimental effect on their mental wellbeing.
More on Parentdish
Suggested For You
Get top stories and blog posts emailed to me each day. Newsletters may offer personalized content or advertisements. Learn more