Up to a thousand boys aged 13 to 16 have disappeared from the school system in north London after their parents sent them to illegal religious schools.
Channel 4's Dispatches and the Jewish Chronicle newspaper have revealed many of the schools - known as 'yeshivas' - in Hackney are "operating illegally and without the most basic health, safety and child welfare checks."
Government documents showed many boys in the Orthodox Jewish community in Stamford Hill, London, "will stop secular studies at the age of 13 or 14 and start attending 'yeshivas' where the curriculum is solely religious.
Between 800 and 1,000 boys aged between 13 and 16 are "missing" from the school system in the borough of Hackney, the papers stated.
More than a hundred boys were filmed going in to an illegal school in Lynmouth Road, Stamford Hill, arriving from 7.30am and leaving late in the evening. It is believed to be one of 12 illegal schools in neighbourhood.
One former pupil at a Hackney school told Dispatches they spoke always in Yiddish - the international Jewish language - and secular subjects were not taught.
He said: "I didn't even know what the word science meant. I hadn't heard this word before."
Another former pupil said: "I was told terrible things about non-Jews."
The Department for Education (DfE) and Hackney Council have been accused of taking a soft approach.
A spokesman for the council said: "Our concerns about these schools date back many years, but we have no powers of enforcement. Any action would have to come from the DfE and we have been working closely with them over several years. That work has so far led to 11 of these 12 schools either being visited by Ofsted, being invited to register or having entered the pre-registration stage.
The DfE said: "This is a long-standing issue that we have been working on with Hackney Learning Trust and the Association of Orthodox Jewish Schools and Organisations.
"There has been some progress and we are working with those schools to ensure that they meet the standards so that they can be registered."
The schools did not comment.