By Gary Eason
Education editor, BBC News website, at the NUT conference
A teacher has described how a 14-year-old girl tried to stab a colleague with a kitchen knife, saying she would kill her.
Delegates say school funding is key
Jenny Cooper, a delegate at the NUT conference, said the girl was disarmed - then went to her class to register.
Incredulous staff were told "we are a special school, we are here to deal with difficult behaviours".
The conference backed her call for risk assessments, and said local authorities needed more resources to help schools.
Ms Cooper was speaking during a debate on deteriorating pupil behaviour.
She said that when an assessment of the girl had been presented to the school's management she had been excluded immediately and both she and her family were given help.
She returned a fortnight later with anti-psychotic medicine and support measures which included eating separately so her knife and fork were away from other children.
A member of the union's executive, Jerry Glazier - who works in a referral unit for excluded children - said the crucial thing was that local education authorities should have the resources to provide this kind of help.
And general secretary Steve Sinnott said later that the way funding had increasingly been devolved to schools was a problem.
"Some of the services that were provided by local education authorities in the past were of an extremely high standard," he said.
There needed to be behaviour support teams of experienced teachers in each area to help schools that ran into difficulties.
After the debate the Department for Education put out a statement saying violence by pupils or parents against members of school staff would not be tolerated.
The department said it would back any head teacher who had to remove or prosecute aggressive pupils or parents.
The government is advocating "zero tolerance" and urging schools to collaborate in tackling poor behaviour.
Jo Lang, a science teacher from Harrow in north-west London, said some youngsters were turned off school because they felt the curriculum had no relevance to them.
"I'm pretty sure that the current national curriculum leaves very little time in any area for us to pause and explore what students are interested in."
The Liberal Democrats make the same case in their approach to school discipline.
The Tories say they would fund a big increase in the number of special units for disruptive children, which they call "turnaround schools".
In Scotland the exectuive is spending £35m over three years to provide greater support for teachers in tackling poor behaviour.
The negative influence of Rooney's use of the vernacular was raised
The NUT called on all political parties to provide schools with the resources they needed.
During its debate another teacher referred to TV chef Jamie Oliver's campaign to improve school meals, and his discovery that better food resulted in better pupil behaviour.
"We could have told the government that," said Pat Astle, from Essex.
"Thirty-seven pence for a school meal is probably less than most people spend on cat and dog food," she added.
"Rubbish in - rubbish out."
Earlier, union president Hilary Bills said in a BBC News interview that the behaviour of some footballers set a bad example for youngsters who idolised them.
Manchester United and England star Wayne Rooney's swearing on the pitch gave the impression such things were acceptable, she said.
Mr Sinnott told journalists this was true of anyone in the public eye.
But it worked both ways: when David Beckham had made an effort to learn Spanish he had praised him for it, he said.