Back in the old neighborhood in North West London after a long absence, I went past the local primary school and noticed a change. Many of my oldest friends were once students here, and recently—when a family illness returned us to England for a year—I enrolled my daughter. It’s a very pretty redbrick Victorian building, and was for a long time in “special measures,” a judgment of the school inspection authority called Ofsted, and the lowest grade a state school can receive. Many parents, upon reading such a judgment, will naturally panic and place their children elsewhere; others, seeing with their own eyes what Ofsted—because it runs primarily on data—cannot humanly see, will doubt the wisdom of Ofsted and stay put. Still others may not read well in English, or are not online in their homes, or have never heard of Ofsted, much less ever considered obsessively checking its website.

In my case I had the advantage of local history: for years my brother taught here, in an after-school club for migrant children, and I knew perfectly well how good the school is, has always been, and how welcoming to its diverse population, many of whom are recently arrived in the country. Now, a year later, Ofsted has judged it officially “Good,” and if I know the neighborhood, this will mean that more middle-class, usually white, parents will take what they consider to be a risk, move into the environs of the school, and send their kids here.

If this process moves anything like it does in New York, the white middle-class population will increase, keeping pace with the general gentrification of the neighborhood, and the boundaries of the “catchment area” for the school will shrink, until it becomes, over a number of years, almost entirely homogeneous, with dashes of diversity, at which point the regulatory body will award its highest rating at last. But none of this has happened in the old neighborhood yet and perhaps will never happen—given its lengthy and proud history of every conceivable form of diversity—and this was anyway not the change I noticed when I passed by.

At the time my particular brand of liberal paranoia was focused elsewhere: I noticed the fence. For this Victorian school, which, for a hundred years, has found cast-iron railings sufficient to mark its periphery, had now added what looked like tall bamboo slats between the bars, as well as six feet of plant life climbing these slats, blocking the view of the playground from…