Teachers' leaders are demanding a code of conduct for school inspections after warning education standards watchdog Ofsted had "lost all credibility".
Delegates at the Association of Teachers and Lecturers' annual conference in Manchester said it was "no longer disliked" but "now disdained".
The debate followed a highly critical report of the inspectorate by the right-wing think tank Policy Exchange, which conclude "a toss of the coin" was just as reliable as an inspector's assessment of a teacher's ability
Pat Kyrou, from Essex, said: "Ofsted, it is not your role to terrify teachers. It is not your role to force teachers to teach in a way that is less beneficial to the pupils.
"It is your role to help teachers give the best education possible to pupils. You can do this by making your inspections professional - making the inspections subject to the same rigour you are applying to the schools."
Simon Clarkson, from Leicestershire, added: "Ofsted is like a big rock distorting the fabric of education.
"The consequences of its decisions, both negative and positive, are so vast, it needs to be infallible. The problem is it is not."
He said he knew of "solid dependable colleagues" reduced to tears because of the stress of Ofsted inspections.
Teachers complained there were too few currently serving heads and teachers on inspection teams - and that retired staff were out of date with modern requirements.
Chief schools inspector Sir Michael Wilshaw has announced he is stepping up moves to recruit more currently serving heads to teams. He also said he was reviewing the role of private contractors in carrying out school inspections.
Questioned about Ofsted, Schools Minister David Laws said: "It is important that we should be ensuring that the quality of these judgements is as high as possible."
He said he was prepared to sit down and talk with union officials about their call for a code of conduct for inspections.