Ofsted will never win any popularity contests with teachers and heated objections to its regime are a perennial of union conference season. But this year's gatherings of the NUT and the NASUWT, held over the Easter weekend, ramped up the hostility, with calls for the inspection system to be boycotted and waves of attacks on chief inspector Sir Michael Wilshaw.
At the NUT conference, the union said it would consider launching a campaign of "non-cooperation" with Ofsted, inspired by similar action taken by teaching unions in Northern Ireland, which could see inspectors barred from the classroom.
Keith Williamson, a teacher from Kirklees, West Yorkshire, was typical in his criticism of the current system as a "blunt, crude, nasty instrument". He claimed that Ofsted paints teachers as "complacent, lazy and failing children", and warned that no-notice inspections would drive school leaders to keep their schools on "constant and unsustainable Ofsted alert".
Mr Williamson said that the time had come to work out how "non- cooperation" could be pursued. "Let's face it, the strategies we have used so far have failed," he told delegates gathered in Torquay. "Does anyone believe that Ofsted today is better than it was in previous versions?"
Martin Powell-Davies from Lewisham, South London, said that boycotting Ofsted should be strongly considered. He said there was excitement among NUT members at the idea that, if visited by an inspector, they could say, "Class, stop what you're doing. We've got an unwelcome visitor and we need them to leave."
Both the Ulster Teachers' Union and the Irish National Teachers' Organisation have implemented similar boycotts with their watchdog, the Education and Training Inspectorate. Members have been instructed not to hand over any documents or data to the inspectorate, and if an inspector walks into their classroom they must stop teaching. Last month, The Belfast Telegraph claimed that the action had plunged the inspection system into "chaos", as it had all but stopped the process in schools where the two unions have a sizeable membership.
The system in England was described as "Orwellian" by one NUT delegate, while another entered into the spirit of Easter Sunday by suggesting that, had Ofsted existed in biblical times, it would have judged Jesus Christ, an otherwise inspirational teacher, to be inadequate.
Teachers at the NASUWT conference in Birmingham were in similarly combative mood. "Can we boycott Ofsted?" asked Derby teacher Jason Cosford. "If not, why not? If we can, why aren't we doing it?" His question received a warm reaction from delegates, but Bryan Cookson, the union's national treasurer, urged caution. "Legally, we just can't have a trade dispute with Ofsted; they are not our employer," he said. But he insisted that the watchdog would indirectly be "hit hard" by NASUWT members' continuing "work to rule" action. Direct action against Ofsted might be tricky to manage from a legal perspective, but unions have overcome such difficulties in the past. The government claimed that the 2010 Sats boycott was illegal, but unions pressed ahead, claiming that it was a legitimate trade dispute.
Sir Michael Wilshaw - who only reached 100 days in the job last week - was also singled out for criticism for taking what the unions viewed as an aggressive stance against teachers.
Christine Blower, NUT general secretary, said that his rhetoric undermined his credibility with teachers and raised concerns that he was "acting as a parrot or puppet for ministers". At the NASUWT, one speaker quipped that his name read backwards sounded like "Sure will, Michael, sir".
Ofsted batted away the criticisms, claiming that nine out of 10 headteachers say inspection is a positive experience that helps schools to improve. "We take into account the school's context and do not expect the impossible. But there are hundreds of outstanding schools serving the most deprived communities - if they can do it, then others can too," a spokeswoman said.
Original headline: `Let's face it, the strategies we've used so far have failed'