Teachers are demanding that schools carry out "risk assessments" of pupils with behavioural problems, to protect other pupils and staff from violence.
By Gary Eason
BBC News Online at the NASUWT conference
They say the risk starts young.
Helen Tunn, a primary school teacher from Oldham, said children as young as four could display "very violent and disruptive behaviour".
"They can wreak havoc in a classroom just as effectively as any teenager," she told the annual conference of the NASUWT teachers' union.
The conference called for research into what it said was the "deplorable" fall in standards of pupil behaviour.
Dave Battye said this was needed to establish whether there had indeed been a deterioration.
He said another teacher who had complained that the behaviour of pupils in school had gone downhill since he was a child was Socrates - in 399BC.
Dave Battye wants spending on research
The research should then seek to establish why things had got worse - and finally what could be done about it.
The conference wanted teacher training colleges and teachers' employers to improve training in behaviour management and conflict resolution.
And it demanded a code of conduct for pupils and parents, to be drawn up by the government "in full consultation with trade unions".
Ralph Robins, a teacher in Cornwall, said that in his school three 10-year-old boys had admitted repeatedly robbing a 30-year-old woman with a mental age the same as their own.
"I found out they had been doing it regularly, and on the last occasion they made her strip off her clothes," he said.
Their punishment included a withdrawal of privileges, which in one case included being dropped from a school football team which had reached the semi-final of a competition and was due to play at Manchester United's ground.
Margarita Taylor was attacked by a parent
The parents of two of the boys were "thoroughly ashamed" - but one set were concerned only that their son was going to miss the match.
They complained to the head teacher, then to the chairman of governors - both of whom had backed his action.
The mother then came back to him saying she would keep the boy off school, which she did for two days - then threatened Mr Robins by saying "You saw how big my husband is".
A union survey in the south-west of England had produced 800 accounts from teachers of aggressive or abusive behaviour, Les Kennedy said.
Primary school violence
Primary school teachers were being sworn at and attacked, secondary teachers being attacked and abused daily:
"Having my fingers bent back", "arm slammed in a door", "objects thrown at me" were some of the responses.
Analysis of the incidents had revealed that they peaked before lunch on Wednesdays.
Andy Mather was punched in the face
Another teacher, Andy Mather, described how he was punched in the face repeatedly when he told two boys to stop fighting.
Despite the attack he said he had managed to stick to a "golden rule" he had been told in his training - never touch a child, or you risk being accused of assault.
Margarita Taylor, who teaches in Southwark in south-east London, demanded tougher action by school managements.
"The adult who attacked me was only banned from the school premises for three weeks," she said.
"I still feel very anxious every morning to find this adult in my playground: What is he going to do next?
"I feel that the system has not supported me."
Ian Draper, a member of the union's executive, told BBC News Online the idea of the risk assessment was to force schools to recognise what was in fact their legal obligation.
Mr Draper says schools have a legal obligation in this area
It was done for premises but not usually for people.
"When we talked to the Health and Safety Executive about this they were reluctant on the idea of risk-assessing individual pupils."
But with pressure from the union more of it was being done, he said.
In his own school, staff had been warned about the arrival of a 14 year old with a tendency to quite violent attacks and other disruptive behaviour including defecating in classrooms.
"You know he is a risk so you assess that, what might trigger it, who is at risk - the other children, the member of staff - and what the school can then do."
Control measures might include giving a student a "minder", removing him from practical lessons because he could not be trusted with tools, and arranging "behaviour modification" sessions.
"It does work, because it identifies the hazard and the level of risk," he said.
On Tuesday the union's general secretary, Nigel de Gruchy, proposed a new law - already dubbed "Nigel's Law" - that would make common assault on public sector workers such as teachers an offence on a par with causing grievous bodily harm.
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