He said: "My illness was caused by the cumulative stress of many years which became beyond my capacity to manage. I tried as a primary head to lead my school in a way consistent with NUT principles, but I always felt bullied by government."
The head of Bentinck school, an inner-city primary in Nottingham struggled to control his emotions as he admitted he had not been open about his illness when he withdrew as the left-wing candidate to lead the union in 2003. He was speaking out now because more teachers were suffering stress problems and to show mental health issues affect normal people in normal circumstances.
Mr Illingworth, 55, a former NUT president said: "In the end the only way to deal with unmanageable stress is to remove the cause of it. I'm removing the cause by leaving teaching. I think I have been a good headteacher but my health comes first." The former NUT president got a standing ovation.
Mr Illingworth, who is married with two grown-up sons, is on sick leave and negotiating early retirement on ill-health grounds.
Lorraine Eytle, a special needs teacher from Waltham Forest, north-east London, said: "It actually scared me and I wonder if people outside teaching realise how serious the effects of workload can be. I have grown-up children who would never go into teaching after seeing the stress I have suffered."
Mr Illingworth's came after delegates voted for a national industrial action ballot against the wishes of the leadership. A national vote was necessary to give teachers in individual schools the confidence to take action where workload was intolerable, delegates said. Jim Miller, primary teacher from Calderdale, said: "I seem to work all my waking hours and as for work-life balance, I've forgotten what a life is."
Alex Douglas Hinsey, NUT divisional secretary in Knowsley, said schools were failing to deliver promised time for planning, preparation and assessment. Teachers going on training courses were being denied PPA time and others were being asked to supervise absent colleagues' classes during non-contact time. "I am angry I have to see good teachers reduced to tears because they cannot cope," he said.
Liam Conway, from Nottingham, warned lesson observations are adding to teacher stress. He had been observed five times since September, twice by Ofsted, twice as part of a school faculty review and once as part of performance management. As head of faculty, he carried out a similar number of observations in the same period. He said: "The increased number of workplace observations is a form of bullying. Teachers are cracking up under the stress of all this."
The conference also backed a motion calling for the "biggest lobby of Parliament for many years" to oppose the new education and inspections Bill. It called for the NUT leadership to investigate where industrial action can be taken if the proposed trust schools or any other measure in the Bill worsened pay and conditions.
But compared with previous conferences, consensus appears to have broken out between the leadership and rank and file.
The harmonious atmosphere was helped by the fact that there was no minister to heckle (none had been invited and would have declined in any case). The emollient approach of Steve Sinnott, the general secretary, and the fact that he has kept the union out of social partnership with the Government and other unions also calmed the seasoned firebrands.
In his keynote speech ending the conference, Mr Sinnott said inviting business to run trust schools could have far-reaching consequences ranging from the curriculum to dress codes.
"Banned from selling fizzy drinks and sweets in vending machines, fast-food companies might return through the back door as trust sponsors and governors. Perhaps they'll want to alter the science curriculum - or the design and technology curriculum to highlight the science of food processing and marketing.
"Or there could be debates about how school uniforms could reflect each trust's interests. The corporate colours of the sponsors would be all pervading - orange and brown, Fanta and Pepsi uniforms."
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