Government and local authorities are failing thousands of children in care, leading child care organisations say.
Charities are calling for action to prevent vulnerable teenagers falling through the care net.
There is particular concern for so-called looked after children between the ages of 16 and 21.
A spokesman for the Department for Children and Families said the Children and Young Person's Bill would give more support for children leaving care.
The UK has more children than any other western European country locked up - about 3,000 compared to fewer than 400 in Italy.
There are no government records for approximately 4,500 children - about 8% of the total 60,000 children in the care system.
Two-fifths of children in care achieve no GCSEs and only a fifth obtains five or more.
Children based in the Midlands interviewed for the BBC's Today programme complained that they were abandoned once they reached 16.
They allege that they were removed from foster care or children’s homes and placed in private rented accommodation.
One 17-year-old girl said: "I found it really hard coming out of care.
CHILDREN IN CARE
3,000 children locked up compared to fewer than 400 in Italy
Two-fifths of children in care achieve no GCSEs
Only a fifth obtains five or more GCSEs
"From being looked after, so if you run off you always have someone to come and pick you up [to a situation when they] haven’t prepared you for the real world.
"They haven’t prepared you for life’s basic skills."
Other children recounted similar experiences of being abandoned to a life of petty crime, prostitution and drugs.
According to the Howard League for Penal Reform, 46% of children behind bars in youth custody have experienced the care system.
Frances Crook, the League’s Director, told the BBC: "We are saying the prison system and the local authorities are not fulfilling their full obligations to look after children properly and there are perversely financial incentives for local authorities to encourage or allow their most difficult and challenging children to end up in prison because they then don’t have to pay for them.
The reality remains that for many young people...they do face life on their own, unsupported in what can be very vulnerable and threatening environments for them
Kathy Evans, Children's Society
"These are children who should be looked after by the state properly but their needs are not being looked after."
All too often, according to Crook, there are no social workers at the prison gate to greet a child entitled to care on release.
The Children’s Society has particular concern for disabled children living away from home and unaccompanied refugee children.
Kathy Evans, the Society’s director, said: "The situation has been changing.
"I think the government does recognise that to expect any 16-year-old - let alone one who has had a disrupted childhood in care - to live on their own and effectively to fend for themselves is really compounding problems.
"The reality remains that for many young people - unaccompanied children arriving at 15 and some young people who’ve only recently come into care at 15 or 16 - they do face life on their own, unsupported in what can be very vulnerable and threatening environments for them."
Many childcare organisations point out that the state is removing children from hazardous situations at home and then effectively placing them in worse situations or conditions that are no better than they had experienced before being taken into care.
The plight of looked after children after the age of 16 is currently the subject of an investigation by the select committee for children, schools and families.
The Department for Children, Schools and Families is currently steering new legislation through Parliament aimed at improving care for children after 16.
The government’s introduced 11 so-called Right To Be Cared For pilot projects.
A spokesman said: "We want young people to be more actively involved in planning their transition to adulthood and ensure that they are effectively supported if needed beyond 21.
"We know that the care system has not treated children in care in the way they deserve to be - that is why our Children and Young Person’s Bill is currently before Parliament.
"The Bill will secure more direct support for children in and leaving care."
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