Teachers who ban slang could cause pupils “long-term damage”, making them feel stigmatised and discriminated against, a linguistics expert has warned.

A new study by Ian Cushing, an education lecturer at Brunel University and expert in applied linguistics, finds policies that ban the use of non-standard English words - such as “bare” and “peng”- have a negative impact on pupils’ learning and can make them feel that their language is “worthless”.

Related: Teaching slang at primary could help fight ‘middle-class’ Sats bias, says academic

Opinion: Non-standard English is not sub-standard

News: Gibb stresses oracy as primary bans the word ‘like’

Dr Cushing interviewed 16 primary school teachers as part of his research, as well as visiting schools and analysing media reports and government policies, finding a growing trend for schools to ban the use of slang. For example:

• One school banned the use of “Yorkshire verbs” and gave Year 7 students the role of “grammar police”.
• Banned words appeared inside “word jail” posters in some primary classrooms.
• One school had produced a policy called “Elocution for Employment”, which described how pupils were “competing” for jobs with Europeans and non-native speakers, encouraging teachers to correct pupils if they “lapse into poor spoken habits” to prepare them for the world of work.
• Many school policies cited the language of popular reality television programmes such as The Only Way is Essex and Love Island as examples of the kinds of speech pupils should avoid.

Dr Cushing said these policies were unlikely to raise standards and could cause pupils long-term harm.

“Banning language and non-standard grammar is a punitive practice which can make people feel stigmatised, discriminated against and that their language is worthless,” he said.

“I think some adults feel threatened by how kids speak, but kids having their own language is a big part of how they form identities and interact with different social groups.

“There’s nothing incorrect or wrong about non-standard language, but a lot of school policies - as well as government policy, grammar tests and guidance for teachers - seem to reproduce the problematic idea that there are ‘right’ and ‘wrong’ ways of using language.”

However, some English teachers argue that schools are a “dry run” for adult life and reinforcing formal language helps pupils.

Lauran Hampshire-Dell, an English teacher, said: “The classroom is a dry run for habits students will need later in life and speech is as important as writing.

“Slang is natural, but students should be taught when it’s appropriate and when it isn’t. One way of approaching this is stopping students when their formal speech lapses in class and asking them to restart their sentence.

“It can take a while, but it is effective for them and their peers - who become aware of their own slips, too. Applied consistently, and paired with giving students the vocabulary you want used, slang quickly disappears.”

Dr Cushing said that standard English “has its place for things like job interviews or ceremonies”.

But he argued that children were adept at code-switching - adapting the formality of their language according to the context - and that policies dictating which forms of language were “correct” revealed a misunderstanding of how language worked.

“They don’t need to have their language policed, they police it themselves,” the academic said. “I am not suggesting students shouldn’t have access to standard English, but they need to be taught why it carries social power, and that using non-standard English is not ‘incorrect’, ‘wrong’ or ‘inappropriate’.”

Pupils who were reprimanded for how they spoke in lessons were less likely to take part in class discussions, he said.

“There’s likely to be long-term damage. Taking a punitive stance won’t teach good standards in any meaningful way.”

He told Tes: “Children need to be taught about the reasons why standard English has so much power - and the current curriculum doesn’t do that.”

Dr Cushing said it was a “shame” that the English language GCSE controlled assessment on spoken language - which encouraged pupils to consider how they adapted the formality of their language in different contexts - had been dropped when GCSEs were reformed from 2014, and that this represented “a lack of opportunity for children to learn about linguistic diversity”.

“There has been a shift towards conservative - both little c and big C - agendas in education, a focus on what’s called knowledge, and this is reflected in language policies,” Dr Cushing added.

The Department for Education has been contacted for comment.