Ifhat Smith’s son was 13 years old when he was questioned by school officials and asked if he was affiliated to the jihadist group Islamic State.

Smith was shocked when she ultimately realised her child had been questioned under the government’s Prevent strategy – but was left baffled when she discovered the interrogation was triggered by his use of the term “eco-terrorist” in a classroom discussion about environmental activists.

The boy was in a French class at his school in Islington, north London, when he used the phrase to describe some images. Nothing was said at the time. He went home, enjoyed the weekend and returned to school on Monday.

“He was in a French lesson, someone came in, said something to the teacher and the teacher pointed at him. They said, ‘follow me,’” Smith said. “He had never been in trouble at school. He was really nervous. There were two women there, one he didn’t know.

“First they made a joke asking him was he a ‘tree-hugging hippy’ but then they asked him if he was affiliated with Isis. Isis wasn’t even a word in his vocabulary. He was terrified. He didn’t know what was going to happen.”

Ultimately, the officers were satisfied that Smith’s son was not the next Osama bin Laden. He was asked to return to class and the subject was never raised again. When Smith’s son returned from school and told her what happened, she immediately called the head of his year group.

“The penny dropped. I said, ‘have you been questioning my son under Prevent?’ She said they had to because of regulations, schools were having to do this. This was such a shock. I’d heard little bits about Prevent, I just thought it’s something so far removed from us, we’re not going to be affected by this.”

The experience of Smith’s son reflects the central concern surrounding the government’s Prevent strategy for years: that it fosters discrimination against people of Muslim faith or background and inhibits legitimate expression.

There have been numerous similar reports over the last 15 years: an eight-year-old questioned by Prevent after his teachers mistook his T-shirt slogan for Isis propaganda, a 17-year-old referred because he wore a “Free Palestine” badge to school and a student of counter-terrorism questioned after an official spotted him reading a textbook entitled Terrorism Studies.

After years of pressure from individuals, campaigners and politicians, the government has finally agreed to address these concerns with an independent review of the Prevent strategy.

One of four strands of the government’s counter-terrorism strategy, known as Contest, Prevent was created by the Labour government in 2003 and its remit was widened by the coalition government in 2011.

Its stated purpose is designed to steer people vulnerable to all forms of extremism away from violence and essentially from becoming terrorists capable of violence. The Channel programme, an arm of Prevent, mentors those identified as at risk of radicalisation. Since 2012 more than 1,200 people had been supported by Channel.

The controversy surrounding the approach deepened in July 2015, when the government introduced a statutory duty on schools, NHS trusts, prisons and local authorities to report concerns about people who may be at risk of turning to extremism or terrorism.

Rob Faure Walker, a secondary school teacher in Tower Hamlets and a PhD candidate investigating the impact of counter-extremism discourses in educational settings, saw the impact of the duty first-hand when children suddenly stopped talking about specific issues for fear they would be targeted by Prevent officers – a so-called “chilling effect”.

Rob Faure Walker. Photograph: David Levene/The Guardian

“The most profound example I had was a kid who was a devout Muslim telling me he was scared of practising his religion in school for fear of a referral,” he said.

Walker said that as a teacher he came to realise that having robust discussions with children on difficult topics – such as those who expressed frustration with western foreign policy or made racist remarks – actually helped ensure such views did not lead to violence.

“In my experience what is now being targeted as extremism was part of the mechanism that pathways to violence were diverted,” he said. “Since then Prevent comes in and starts to specifically target those types of conversations, putting a duty on me as a teacher to report those conversations as extremism – and it’s based on a false premise that the airing of extreme views is a predictor for violence.”

Longstanding critics of Prevent have cautiously welcomed the review, which will be launched within six months of the government’s counter-terrorism and border security bill passing into law.

Yasmine Ahmed, the director of the NGO Rights Watch UK, which in 2016 produced a landmark report on the impact of Prevent, said it was essential for a full and transparent review to took place to ensure its legitimacy.

“We think it’s essential given serious human rights concerns – particularly the impact on children in schools,” she said.

“The Prevent strategy is not a hard security measure, we’re not talking about torture. However, it’s incredibly pervasive. It affects whole communities. Parents aren’t talking to their children about political pressures or Islam because they were worried about what the children might go on to say at school. It is hugely chilling. It promotes a form of self censorship.”

She added: “Prevent has alienated and marginalised the community who are now mistrustful of the security apparatus that needs them to work with them.”

Miqdaad Versi, assistant secretary general at the Muslim Council of Britain, said one of their core concerns with Prevent had been the lack of a means of testing or proving its success. He said: “If you have a strategy it should have the appropriate controls to see if it’s effective. It’s standard practice. That’s a core part of our concern.”

Rachel Logan, legal expert at Amnesty International UK, which has repeatedly called for an independent review, said: “Prevent has always looked to be a highly dubious scheme built on shaky, almost evidence-free foundations, and we need to see a review that properly assesses its impact and approach.”

Prevent is not without its supporters, however, including significant, influential voices within counter-terror circles. Announcing the review, the security minister, Ben Wallace, challenged critics of the strategy to produce solid evidence of their allegations, accusing them of “distortion and spin”.

Richard Walton, who was head of Scotland Yard’s counter-terrorism command from 2011 to 2016, said: “The implementation of the government’s Prevent strategy has undoubtedly resulted in lives being saved that would have been lost from terrorist attacks had interventions not taken place. It comes as no surprise, therefore, that the strategy has traditionally been opposed by extremist and terrorist groups who want to undermine the government’s efforts to prevent terrorist attacks.

“I question whether a review commissioned by the Home Office of its own counter-terrorism strategy is really necessary and value for money at this time when the threat from terrorism remains severe, which means a terrorist attack is highly likely.”

But the emotional and psychological impact on those who believe they were wrong to have been quizzed under the Prevent strategy is clearly damaging.

Smith said of her son’s questioning. “He was just so happy with the school. He felt so comfortable. When this happened it really made him check his identity and how people see him.”