Nearly half of the home-educated children in some areas of England receive an unsatisfactory or non-existent education, according to the first official statistics on the subject released last week.
The figures show that nationally nearly 10 per cent of children who are not in the school system are not receiving an acceptable education.
But this figure - produced from a survey of local authorities - rises to 45 per cent in Stockton-on-Tees, 23 per cent in Wolverhampton and 24 per cent in Leeds. By comparison, the latest Ofsted figures report that just two per cent of teaching in schools is considered "inadequate".
The figures provided by the Department for Children, Schools and Families only accounted for 11,600 children who are taught at home, but estimates from the lead home-educator group, multiplied by the total number of children in the country, would suggest a total figure of at least 23,000 .
The publication of the new statistics comes as the Government presses ahead with plans to make parents who take their children out of school register with local authorities and give details of how and what they will teach.
Currently, parents who decide to home educate their children are not required to teach them full-time and local authorities do not have to monitor how many hours each child receives and over how many weeks. Home educators do not need to teach for the same number of hours as a state maintained school.
Officials at Leeds City Council said many home-educating parents "hide behind the law" and some children are "never seen" after being taken out of school. Others use it as a way to avoid being prosecuted for truancy, according to Brian Hogg, who is responsible for "education other than at school" services for Education Leeds.
"We see a wide range of provision, from professional parents with the finances to provide tutors and laptops, to families who don't take education seriously," said Mr Hogg.
Home education support charity Education Otherwise disputed the accuracy of the statistics, saying local authorities were not given enough time to collect the data.
"Despite this, the DCSF has taken the information at face value, even though it doesn't really tell us anything because it's a mess," said Fiona Nicholson, government policy group chair at the charity.
"The assessments from local authorities are completely subjective, and this means plans for registration will open a can of worms."
Ofsted officials have now started their first study into home education. The inspectorate's review into special educational needs will also look at the issue of children being taught by parents because they can't get specialist help in mainstream schools.
Local authority officers currently being trained to work with parents of SEN children, as a result of the Lamb inquiry, will also get guidance on assisting home-educating families.
Hardip Begol, deputy director of the SEN and disability division at the DCSF, said in a letter to local authorities this week that they will get more funding to allow home-educated pupils to use school services and take GCSEs as private candidates.