Rachel Wolf is a partner in Public First. She was an education and innovation adviser at Number 10 during David Cameron’s premiership, and was founding director of the New Schools Network.

I live three streets from where I grew up in London.  I walk past my old primary school every day. Physical proximity to childhood offers a daily reminder of what we have achieved in education over the last generation (at least in London).

The nearest secondary school to me when I was a child was – like many in the central part of the capital – a no-go area. It was rife with violence, which often spilled out into the streets. Kids from other schools and adults were mugged. Middle class parents were desperate to avoid sending their children there – often moving out of the area as soon as those children approached eleven. I remember vividly our end of year primary school concert ,which was held at that school: boys would stand at the windows of the hall, stubbing cigarettes out on the window while powerless and cowed teachers looked on.

This wasn’t that long ago. A time when Britain was – as now – a rich and developed country. And yet that school, like so many others, is now transformed. Closed down and turned into an “outstanding” academy, it is now a desirable destination for the wealthier parents in the area, as well as those from nearby social housing.

It really matters that schools are not only good, but environments where parents of all backgrounds are willing to send their children. One of the most, in my view, nonsensical criticisms I used to get about new Free Schools was that they didn’t have a high enough percentage of children on free school meals. My argument was always that if these schools were truly mixed – that parents who had previously fled the area were now willing to send their children there – this was a cause for celebration, not sorrow.

I am now very worried about the future of these new, transformed schools. Not because of education policy, or because the heads and teachers are any less remarkable, but because the violence that has erupted in London – and that is so dominated by teenager-on-teenager knife crime – is going to make them no-go zones once again.

To be honest, until recently attention to knife crime has been limited. It has sometimes felt that this is because it is happening to ‘other people’s children.

That won’t hold. Already, I hear whispering from worried parents. Children are being checked outside the school grounds for knives. Some are in gangs. Do I want my kids in this environment? What if something goes wrong?

We spend a lot of time in education at the moment debating such matters las mental health, character, sex education. If our schools stop being safe – or even stop being perceived as safe – all of that will be completely irrelevant. We often take for granted that the state will operate effectively as a ‘monopoly of force’. But if the minute that fails, then the rest of our public services fail too.

As is often the case, both the blame and the solution for knife crime has been lain at schools’ door. The reason this has happened, it is argued, is because schools have ‘excluded’ (temporarily or permanently removed them from school) children for bad behaviour.

I’m sure it’s true that there are some schools that have been overzealous in removing kids. But in general, it is wholly acceptable and right that schools should remove children that are a danger to others and who are preventing other children from learning. And anyone who has talked to a teacher who has had an exclusion decision overturned, and had to try and cope with a pupil who knows that teachers’ power to stop their behaviour is zero, would be sympathetic to exclusions.

And at the same time, the evidence that this is leading to knife crime is highly dubious. Research by the Ministry of Justice has found that only “a very small proportion [of pupils] committed the knife possession offence shortly after being excluded”. Many were excluded after they were found to have knives. Others committed a knife offence several months after an exclusion. It’s difficult to show that it was the act of exclusion itself in either of these types of cases which caused the pupil to commit the act.

Nor is the solution to add something else to the schools’ curriculum. This is always the lazy proposal for every policy problem – get schools to teach about it! The campaign Parents and Teachers for Excellence has found 34 articles with different calls on the curriculum this year alone.

The much harder – but better – policy solution is to improve where such excluded children end up. Each local authority has a responsibility to educate every excluded child, either by placing them in another school, or by putting them in what is called “alternative provision” – essentially much smaller institutions which work with pupils who for whatever reason can’t engage in mainstream education. These schools, despite dealing with some of the most challenging children in society, vary enormously in quality and are often bottom of the priority list. This should change.

At heart, we also need to recognise that this problem is not an educational one: our schools are much, much better than they used to be. They are all under terrible threat because of violence that is happening outside some of their gates – and if it isn’t sorted it will destroy the hard work of the last two decades.