The union also called for an end to the automatic suspension of teachers facing accusations from pupils of abuse.
The demands come after Marjorie Evans, a headteacher and NUT member in Caldicot, Gwent, was suspended for 13 months before being cleared of assaulting a pupil.
The union's threat was made more potent by a high court decision to allow school governors to take into account strike threats by staff fearing for their safety when considering the circumstances of readmitting a pupil banished for violent behaviour.
The NUT reported that the number of teachers interviewed by police on assault allegations was normally around 120 annually but that figure was expected to rise to 170 this year. Only three or four cases reached court, it said.
The NUT said it was prepared to take industrial action to protect teachers and pupils if headteachers failed to act or an appeals panel reversed an exclusion. Headteachers should expel any pupil who needed to be restrained except in "exceptional circumstances".
John Bangs, the union's head of education, said: "The severity of bad behaviour has got worse. There's a small group of children whose behaviour is qualitatively worse than it has been in the past."
Mr Bangs acknowledged that the union's stand was a toughening of its public position on exclusions, although he said the union had always defended individual teachers who were victims of violence.
