Teachers vote to boycott individual violent pupils
Pupils have been so violent or disruptive that on eight occasions last year teachers held ballots to refuse to teach them in their classes.
These votes, by members of the NASUWT teachers' union, included cases where pupils had assaulted teachers but had been allowed to stay in school.
In response to these ballots, pupils were expelled or moved.
Schools minister Nick Gibb said teachers had been given "the backing they need to tackle poor behaviour".
NASUWT leader Chris Keates says the trend reflects worsening behaviour problems.
The number of these "refusal to teach" ballots, across the UK, has risen for the third successive year - up from three in 2012, four in 2013 to eight in 2014.
The teachers' union, holding its annual conference in Cardiff, says there were even more cases where a ballot was threatened, but alternative arrangements were made for disruptive pupils without the ballot going ahead.
Among incidents triggering ballots were cases such as a 16-year-old pupil in the west of England who had assaulted pupils, teachers, the head teacher and the police when called to assist. After a ballot by teachers, the pupil was "educated off-site".
In a secondary school in north Wales a teenager with a history of disruption had threatened to "slit the throat" of another pupil. After a ballot by teachers, the pupil was expelled.
A teenager at a secondary school in the English midlands, who the union says had assaulted and threatened staff and pupils, stayed in school but was barred from attending classes taught by NASUWT members.
In another case, the union says a ballot followed a dispute over how a group of teachers intervened with a pupil with a history of attacking others.
When there were allegations that teachers had "assaulted" this pupil there was a "refusal to teach" ballot, after which the pupil was removed from the school.
Ms Keates says schools face a "widespread and increasing problem of pupil indiscipline".
The union asked its members about their experiences of pupil behaviour, receiving about 3,500 online responses.
Almost three quarters of respondents claimed there was a "widespread behaviour problem in schools today" - a higher proportion than in a similar survey last year.
This is not a representative sample, but among those replying, 82% said they had faced verbal abuse from a pupil and 38% from a parent in the past year. Some 23% had been physically threatened by pupils and 16% "assaulted".
According to those who responded, the biggest contributor to declining behaviour is an "excessive focus on data-driven targets", identified by almost two thirds of teachers.
Ms Keates also blamed increasing class sizes and "the lack of support for children with special needs in mainstream schools".
The conference will debate pupil indiscipline on Saturday.
It will hear claims behaviour standards are being undermined by a "blame culture in schools that seeks to hold individual teachers responsible for poor pupil behaviour, whilst overlooking the critical role that school leaders should play".
The motion will also criticise a lack of consistency in how rules on behaviour are applied.
School reform minister Nick Gibb said: "The Conservative party is committed to giving schools the backing they need to tackle poor behaviour. That's why we've made it easier to search pupils, brought back same-day detentions and clarified teachers' power to use reasonable force.
"We've also made sure that a head teacher's ability to exclude pupils isn't undermined by external bodies. As a result, three quarters of teachers now rate behaviour in their school as good or better."
A Liberal Democrat spokesman said: "It is vital that teachers have the resources they need to manage behaviour and support those children who need extra help.
"This is exactly why, in government, Liberal Democrats protected school budgets and introduced the pupil premium - extra money to support the children most likely to struggle in class."