The growing popularity of “zero tolerance” policies towards bad behaviour in schools is “feeding a mental health crisis” among pupils, teachers have complained.

Headteachers are taking an “increasingly punitive” approach to discipline including the use of detention, isolation and exclusion for students who break rules, delegates at the National Union of Teachers’ (NUT) annual conference were told.

Jonathan Reddiford, a delegate from North Somerset, said that in some cases, imposing a “zero tolerance” behavioural policy is “nothing short of child abuse”.

He told of a female pupil who was “kicked out” of school for speaking on her mobile phone, which was against the rules.

“She was speaking to her mum who was in the military and had been deployed to Iraq,” Mr Reddiford.

“It was the first time she had spoken to her mum for 30 days and she gets kicked out because of it.