One of the UK’s biggest teaching unions has called on the government to ban social media for under-16s over concerns about mental health and concentration.

The Teachers’ Union (NASUWT) wants legislation to be tightened so big tech firms would face penalties for allowing children to access their platforms.

The online safety debate was thrust back into the spotlight this month when it emerged Elon Musk’s Grok AI tool was digitally removing the clothing of women and children.

A pioneering social media ban for under-16s came into force in Australia last month, but its effectiveness has yet to be established.

NASUWT said there was increasing evidence that unregulated access to social media was detrimental to children, affecting behaviour in school and harming mental health. It also said children were being harmed by exposure to violent and sexually explicit content.

The union’s general secretary, Matt Wrack, said: “Teachers are dealing every day with the fallout of a social media landscape not originally designed and not suitable for children. Social media companies have shown time and again that they will not act responsibly unless they are forced to do so.

“If we are serious about safeguarding children, protecting their mental health and combating the behaviour crisis in our schools, then a statutory ban for under-16s must happen urgently.”

Some education leaders have previously suggested that mobile phones should be banned in school buildings.

The education watchdog, Oftsed, has also said social media is “chipping away” at children’s attention spans and aggravating bad behaviour.

NASUWT research found that an overwhelming majority of teachers had reported an increase in the number of pupils exhibiting violent and abusive behaviour last year. It surveyed 5,800 of its members, and 81% had noticed a rise.

The survey also asked teachers if they thought social media was a driving force behind deteriorating behaviour, and 59% agreed it had contributed.

When the union conducted a separate poll of 300 members, asking if they would support a statutory social media ban for under-16s, 89% said they would.

“Our members tell us that social media is now one of the biggest drivers of poor behaviour, anxiety and disengagement in the classroom,” Wrack said.

“Children deserve the chance to grow, learn and form healthy relationships without being pulled into an online world that profits from their vulnerability.

“We believe the government should join other countries and help children and young people by moving to a ban which would have widespread support among parents and teachers.”

A government spokesperson said: “We support headteachers to take the necessary steps to prevent disruption in our schools – backed by our guidance, the vast majority already restrict the use of phones in the school day, so they do not disrupt learning.

“Through the Online Safety Act, we have taken some of the boldest steps anywhere in the world to ensure children have age-appropriate experiences online, mandating that social media companies protect under-18s from harmful content. We are striking the right balance: protecting children from harm while ensuring they can benefit safely from the digital world.”