Heads are fuelling bad behaviour in the classroom by refusing to punish pupils sufficiently and failing to support staff, delegates at the NASUWT annual conference will hear next week.
School leaders are unwilling to face up to the "unpleasant" problem of unruly children, and their reluctance to discipline pupils has left some schools "ghettoised" and abandoned by middle-class parents, a motion will claim.
Members of the union at Darwen Vale High School in Lancashire went on strike this month, along with NUT colleagues, claiming they were not supported by their headteacher even though children had challenged them to fights, shoved them and made malicious allegations.
At the NASUWT conference over the Easter weekend, delegates will call on Ofsted inspectors to demand that heads use "adequate sanctions" to deal with bad behaviour.
"We have removed, quite rightly, serious sanctions like corporal punishments, and exclusion is only used rarely, but we have not replaced these punishments," said Shane Johnschwager, NASUWT secretary for Brent in north-west London, who is putting forward the motion.
"Ofsted inspectors are easily fooled when it comes to behaviour. When they visit, management are very visible and this encourages order. But when inspectors go, school leaders revert to type - many seem more interested in career development rather than supporting teachers.
"In far too many schools there are no effective sanctions. We need a new approach . We need to get inspectors to hold heads to account."
Mr Johnschwager will tell the conference that bad behaviour in schools deters middle-class parents from sending their child to their local primary or secondary. This leaves the school "ghettoised" and leads to widely varying standards of behaviour in different areas.
"Middle-class parents are more likely to hold schools to account over issues such as behaviour; the loss of their involvement means behaviour in the school might get worse," he said.
NASUWT general secretary Chris Keates said: "Too many teachers say that when they seek support from senior managers about behaviour issues, the response is either to question their competence or condemn their lessons as boring."
Association of School and College Leaders general secretary Brian Lightman said: "The maintenance of high standards of behaviour can only be achieved by a team effort."
HEADS IN THE SAND: Discipline `should be a priority'
Last week, one of the country's most celebrated heads claimed too many headteachers are not making behaviour enough of a priority to improve their schools.
Sir Michael Wilshaw, principal of Mossbourne Community Academy in Hackney, east London, said: "If heads did put behaviour high on their lists, particularly those in tough schools, and dealt with it effectively, (they would see) staff attendance improve, staff turnover also improve and behaviour become less of an issue."
Original headline: Union's warning to heads: you must face up to bad behaviour