The number of disputes involving teachers refusing to teach violent and disruptive pupils has almost trebled in three years, according to a union.
The NASUWT teaching union says that poor behaviour has now become the second most serious concern among teachers after workload.
Current disputes include teachers at one school refusing to teach a Year 10 boy who sexually assaulted a female member of staff.
Those at another school staff are refusing to teach a Year 9 girl who had been urinating throughout the school, often in front of staff, and defecating around the school, wiping it on school equipment.
Both cases resulted in refusal-to-teach ballots, which are among 14 currently being dealt with by the union.
NASUWT general secretary Chris Keates said there were “many more” cases where the union had only threatened to ballot for industrial action, which had resulted in appropriate measures being taken by the school.
She said: “In a lot of circumstances it’s a school which has not got a proper behaviour policy in place and there is general disruption, or else it’s a school where it’s down to one or more pupils, often with special needs, that are wrongly placed in that school but there’s no external support because their local authority’s behaviour support has been cut and there’s no spaces in the referral units.
"It’s mainly secondary schools but not exclusively. Pupil behaviour has always been in the top five concerns for teachers but for the last three years it has been in the top three and last year it moved to the second most serious concern after workload. It overtook pay.”
The union’s figures show there were just three refusal-to-teach ballots brought in 2015, rising to eight in 2017. Of those, all resulted in "action-short-of-strike action" by teachers in which they refuse to cover for absent colleagues or do voluntary activities and stick rigidly to their contracts - at the same time as refusing to teach the violent or disruptive pupils in question.
All disputes from 2017 are ongoing apart from one where a school was said to have "responded quickly" through meetings and discussions following an incident in which Year 10 male pupil with a history of poor behaviour threatened to punch a male teacher in the face and was verbally aggressive and pushed him.
The union says it will release the number of refusal-to-teach ballots brought in 2018 shortly before its annual conference at Easter. But it says there are currently 14 such ballots in place, including eight in relation to refusal-to-teach individual pupils and six over refusals to teach groups of pupils.
A Department of Education spokesperson said: "Teachers and school staff have a right to be safe while doing their jobs and any form of misconduct, including violence towards them, is completely unacceptable.
“We have already made great strides in empowering teachers to tackle bad behaviour and have recently announced a £10 million investment to support schools to share best practice in behaviour management.”