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. Although just one in 20 Muslim children attend them, the proportion is rising fast. And there’s 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 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 benefitted from the Conservative party’s “free schools” programme, which lets a wide variety of organisations set them up. There are now 101 non-Christian religious state (i.e, ‘aided’) schools in England.

Their growth redresses what some saw as an injustice. Whereas Christian families could get free religious education in church-run schools that have long been a part of the state education in England, followers of the other faiths usually had to go to fees-levying private schools. But the boom in religiously selective schools sits oddly with another government aim, to deepen community integration. Earlier this year, prime minister Theresa May called on the country at large to “do more to confront the segregation that can divide communities”.

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.

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. The Tauheedul Islam Girls’ High in Blackburn is the most successful state school in the country, according to the government’s Progress 8 to score, which measures academic improvement from age 11 to 16.

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.

Meanwhile, 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.