All 38 schools run by an evangelical Christian sect that considers television and computers to be evil have been backed by government inspectors.
The Office for Standards in Education confirmed this week that it was satisfied that the entire stock of private schools owned by the Exclusive Brethren provided a good standard of education.
The findings come in spite of growing fears that some private faith schools which do not have to follow the national curriculum fail to promote tolerance and understanding of other cultures.
The Exclusive Brethren, a radical offshoot of the Protestant Plymouth Brethren, believe that the world is the domain of the devil and that children should be taught in safe places away from damaging influences.
Pupils are denied access to modern technology and work in Brethren-run businesses such as packaging manufacturers and publishers after leaving school.
The sect's 15,500 followers in the UK must abide by a strict behaviour code, and socialising outside the sect is strictly forbidden.
This week, Ofsted confirmed that it had completed initial inspections of schools run by Focus Learning Trust, an educational group set up by the Brethren, and recommended all 38 schools in England for government registration.
Ofsted said the Brethren's schools satisfied the registration criteria required of all private schools by the Department for Education and Skills, including provision for pupils' social and cultural development and teaching standards.
Independent schools are also judged on the suitability of the school's owner and the procedures for health and safety, buildings and complaints, and could face closure if they fail to meet the required standards.
Ofsted's announcement follows praise for Brethren schools by David Bell, the chief inspector, in his annual report earlier this year.
Mr Bell said Focus Learning Trust provided "good support to its schools" and the quality of teaching was "generally good", although he reserved criticism for some Islamic faith schools for failing to promote social cohesion.
Caroline Horn, head of the Brethren-run Copsewood secondary school, in Coventry, which has 80 pupils, this week welcomed Ofsted's conclusions.
Neither she nor her 10 teaching staff are members of the sect, but the school has a nine-strong Brethren trust board.
The school teaches the national curriculum, with notable exceptions. There is no sex education or ICT, and fiction that includes references to sex is banned. RE is replaced with Bible studies that make no reference to other faiths and are led by member volunteers.
Miss Horn said: "Almost without exception, the pupils are happy, well-adjusted young people who are keen to learn.
"In comparison to other learning establishments, these children actually listen to their teachers, and show respect in return. Discipline problems are minimal and there is full parental support."
In the past, Brethren children were taught at home or in state schools before the sect's own small schools emerged during the 1990s. The arrangement was formalised with the creation of the Focus Learning Trust in 2003, which merged a series of smaller schools to form the current 38 schools in England. It also has two schools in Scotland, one in Wales and two in Ireland.
Around 1,500 children are now educated by the trust, with parents paying whatever they can afford towards fees.
Humphrey Dobinson, a retired English teacher, used to work at a Brethren school in Swindon. He said: "It is easy to be dismissive of the Brethren, but they bring their children up to be very balanced, understanding young people.
"In terms of their schooling, I admit that I would like to have seen a more balanced curriculum at times. There is only a very basic teaching of biology and they are obviously not keen on learning about other religions, but otherwise children get a normal schooling."
But former members of the Brethren have spoken of being ill-prepared for life outside the sect. Members who leave are officially "shut-up", ostracised for life by the rest of the Brethren "family".
One former member, who left in 1984, aged 18, said: "If expulsion is legal, then the very least they should do is allow the young to be adequately educated to survive the outside world.
"Typically, young people who leave do so with a poor education, poor social skills and are generally ill-equipped to survive normality. Many are vulnerable, emotionally traumatised or suicidal."
Jill Mytton, of South Bank university, is a former follower. She surveyed 295 former members as part of an academic study five years ago.
She found that 30 per cent had symptoms of mental illness, including feelings of alienation and a lack of interpersonal skills.