Scotland's Commissioner for Children and Young People, who produced the research, has called on the government to review the system, and ban the use of bed and breakfast accommodation for those leaving care.
Kathleen Marshall said she was shocked at what she found in her research and the difficulties the children found themselves in. She warned that with increasing numbers of children in care, more and more young people will struggle to cope with the realities of full independence.
The report highlights the gulf between children brought up with their families – who are increasingly staying at home until well into their twenties – and those who are in care.
Although Scottish Government policy dictates that children should leave at 18, six times as many are leaving at 16, often coerced by social services.
The report found that children with "challenging behaviour" are those under most pressure to leave.
Mrs Marshall said they had independence thrust upon them without the skills such as cooking, cleaning and shopping.
The report states that the level of 15- to 18-year-olds who are homeless "represents a shocking failure in corporate parenting".
It claims authorities are either failing to keep under-18s within the care system, or not supporting them afterwards in accordance with the legal duty that extends to the age of 19.
Mrs Marshall said that although the laws and the policy in place supported the children and prioritised their interests, there was a gulf between that and practice.
In 2007, there were 14,000 "looked-after" children, an increase of 26 per cent since 1999 and the highest number since 1982.
Heather Gray, the director of Who Cares? Scotland, which supports children in care, said they spoke of needing help beyond the age of 16.
Tam Baillie, the assistant director of Policy and Influencing at Barnardo's Scotland, said: "Nowadays, most young people stay at home well into their twenties, yet most looked-after young people leave care aged 16 or 17. We need to ask ourselves why our most vulnerable young people are expected to be fully independent at such a young age, often in very difficult circumstances, as the report highlights. It simply is not good enough – we need more progressive practices that significantly increase the average age of leaving care."
A spokesman for the Scottish Government said it was working with councils to ensure care-leavers were housed appropriately and had made clear people should stay in care until aged 18 if it is in their best interest.