Teachers 'too scared to use the red card',
Some teachers are reluctant to use sanctions against misbehaving pupils in case they find themselves in trouble, a teachers' conference has been told.
The NASUWT union, meeting in Bournemouth, says some teachers have found their ability as a teacher questioned after reporting children.
Delegates described children smoking in class or plotting gang-related crimes in school.
A survey of union members found one in seven had been physically assaulted.
And eight in 10 said they had been verbally abused by a pupil in the past year, according to the self-selecting survey, which was carried out online and by post between February and March this year.
About 12,000 teachers from across the UK responded to the questionnaire, the NASUWT says.
David Morgan, a teacher from Lincolnshire, told the conference teachers had been put on "capability measures" after reporting pupils.
"Some schools have a yellow or red card system and I have known members of staff criticised for over-using the red card," he said.
"So they therefore ignore it and the problem goes down the line to the next lesson."
Birmingham teacher Maria Hesson described cases where pupils had "threatened teachers with assault and violence", "invaded personal space" and smoked out of the window during lessons.
There had also been "gang-related issues" in the classroom, she said, where pupils had apparently been plotting to take other children's mobile telephones.
She said teachers in one Birmingham school had gone on strike because their managers did not accept there was a problem with discipline.
"If the government fails to support teachers, classrooms will become battlegrounds and teaching and learning will suffer," she said.
Union executive Paul Desgranges, from Sheffield, told the conference one head had told pupils at a school assembly that if they were behaving badly, it was because their teachers were "not reaching them".
"The same head introduced 'Wow Wednesdays", he said, "where you let your hair down", but one pupil had arrived at a maths lesson and said he was not doing it because of that.
Head teachers' leaders have rejected claims they are not doing enough to support classroom teachers to tackle bad behaviour.
Russell Hobby, general secretary of the National Association of Head Teachers, said: "Given that 80% of head teachers still teach in the classroom on a regular basis, NASUWT's comments are wide of the mark.
"Of course it is critical that senior leaders back their staff, and that's exactly what the vast majority do, which is why behaviour in our schools is steadily improving not declining."
A spokesman for the Department for Education said: "Disruptive or violent behaviour has no place whatsoever in the classroom. That is why we have strengthened teachers' powers to put them back in charge.
"Our guidance also makes clear that teachers can use force to remove disruptive pupils from the classroom when necessary."