These big fences went up while my DS was in primary school. It was shortly after a spate of terrorist threats against primary schools.
There were a lot of letters delivered to the primaries one morning saying that a random assortment of them would be attacked. It was at the same time as we were having a lot of extremist attacks with suicide vests so the teachers were very nervous about it indeed.
I remember our lovely headmistress standing outside the front door with her umbrella, trying to look fierce. That was all she could do really.
The kids had to have lockdown practices where they all got under their desks to avoid gunmen. That was before "lockdown" became the thing where we all stayed at home for covid.
Shortly after that we have an ofsted report that said the school were having continual problems with vagrants just wandering into the school building and them not being able to stop it.
Another time a man with a gun was spotted in the bushes just out side the fence. We never found out if that was a real thing.
A few months later, the massive fences went up.
Hilariously, then school then got a bad ofsted report because they had a firebell during the inspection, and the kids and adults had forgotten how to do fire evacuation or turn off the fire bell. Poor souls. They must have been knackered from dealing with so many different kinds of possible emergency.