A S THE HEAD teacher at a Hindu secondary school, Simon Arnell might be expected to have a sophisticated understanding of the religion. And one day he might. For now, he relies on regular tutoring sessions with the head of the trust that runs his school. Mr Arnell was hired for his academic expertise, not his religious knowledge. The aim, he explains over a vegetarian school lunch of curry and fresh fruit, is to get his establishment to the same position as some Christian schools, where people say: “Yes, it is a faith school. It’s also just a really good school.”

Avanti House in Stanmore, north London, is one of a new generation of religious schools. Some 94,000 children in England now attend a non-Christian religious school, up from 64,000 in 2011. Over the past two decades the number of Jewish schools has more than doubled and the number of Muslim ones has roughly sextupled. As a result, around six in ten Jewish children attend a religious school. Although just one in 20 Muslim children do, the proportion is rising fast. And there is a small but growing band of Sikh and Hindu schools. A religious education is no longer the rarity it once was for non-Christians.

Most of the recent growth has been in the state sector. Since the 1990s governments have encouraged minority religious groups to set up their own faith schools, which are funded by the state but allowed to select pupils on the basis of their religion. A few opened under Tony Blair’s first Labour government in 1997-2001. Since 2010 faith groups have benefited from the Tories’ “free schools” programme, which lets a wide variety of organisations set them up. There are now 101 non-Christian religious state schools in England.

Their growth redresses what some saw as an injustice. Whereas Christian families could get a free religious education at one of the church-run schools that have long been a part of state education in England, followers of other faiths usually had to go private. But the boom in religiously selective schools sits oddly with another government aim, to deepen religious integration. Earlier this year Theresa May called on the country at large to “do more to confront the segregation that can divide communities”. Faith schools, by definition, divide communities by letting schools pick pupils on the basis of their religion. Those that opened after 2010 may select half their intake on religious grounds if they are oversubscribed; those that opened earlier can select more.

Non-Christian faith schools, in particular, seem also to deepen ethnic segregation. No nationwide data are available on the religious make-up of schools. But according to SchoolDash, a data-analysis firm, non-Christian secondary faith schools are more than three times as likely as non-faith schools to be ethnically segregated (measured by comparing their ethnic composition to that of other local schools), and a bit less likely to teach poor children. Avanti House is unusual among faith schools in that it does not explicitly select pupils on the basis of religion. Still, only a couple of pupils in each year group of 180 or so come from non-Hindu families.

Parents pick religious schools for varying reasons. Among Jews, the move to faith schools was prompted by worries over the loss of Jewish culture, more mixed marriages and, in some cases, unhappiness with mainstream provision, says Jonathan Romain, a rabbi who campaigns against faith schools of all types. The feeling from the 1970s onwards was that, having been “Anglicised”, the Jewish community “now needed to be Judaised”, he explains.

Parents with very strong religious beliefs of any sort are likely to turn to the private sector, where schools are more lightly regulated. According to the Institute for Jewish Policy Research, a think-tank, 87% of Orthodox Jewish schools are private, compared with 15% of mainstream Jewish schools. Ofsted, the schools inspectorate, has also drawn attention to the phenomenon of illegal, unregistered schools, which offer dogmatic religious education to children whose parents falsely claim to be teaching them at home.

Some therefore suggest that religious state schools should encourage integration, by drawing pupils away from more doctrinaire private schools. Ghulam Abbas, an education consultant who previously worked at the Department for Education, says the growth of Muslim state schools has encouraged private ones to turn their attention from religious to academic instruction, as parents increasingly expect both to be of high quality.

Indeed, many religious state schools have a sparkling reputation. Tauheedul Islam Girls’ High, in Blackburn, is the most successful state school in the country according to the government’s “Progress 8” score, which measures academic improvement from the age of 11 to 16. On average, pupils at non-Christian faith schools seem to make a bit more progress than those at schools with a similar intake (even if the small sample size means these results should be treated with caution).

But religion sometimes feeds into the teaching of other subjects—in a few cases extraordinarily so. A recent inspection found that at Yesodey Hatorah, an Orthodox Jewish girls’ state secondary in London, staff did not teach reproduction (human or animal) and had censored textbooks to remove images featuring exposed ankles, chunks of “Sherlock Holmes” and much else. Ofsted considered the school “inadequate”, but acknowledged that parents approved of the way it was run. The school accused Ofsted of following a “secularist agenda”. Since England has no syllabus for religious education, provision often depends on the whims of head teachers, says Linda Woodhead of Lancaster University. The subject “has become a dark hole in schools”, she says.

One hope is that non-Christian schools will become less segregated as parents of other faiths and none become accustomed to them, just as many non-Christians are willing to send their children to Church of England schools. That may take a while. In the meantime, children at Avanti House report that they mix with non-Hindus outside school—on the football pitch, for instance. And Claudia Kitsberg of the United Synagogue, which runs ten Jewish state schools, argues that worries of segregation are overblown, given that children spend so much time mixing with a diverse bunch on social media.

But that may not be a perfect substitute. And as the number of religious schools continues to grow, fewer children will come into regular, humdrum, day-to-day contact with those of different faiths.