There is a shortage of child mental health beds
Mentally ill children are still being failed by the NHS in England, the children's commissioner says.
Sir Al Aynsley-Green acknowledged progress since his audit 18 months ago but said there was a "long way to go".
By 2010, the government wants under-18s on adult wards only if appropriate. Of over 200 NHS trusts surveyed, just 15% had all children on the right wards.
The government said an extra £1.2bn towards mental health services meant care was improving.
Sir Al's report Pushed into the Shadows, published in January 2007, criticised the "national scandal" whereby many children were being treated on adult psychiatric wards because of a shortage of beds.
The government has now set a target that by 2010 no children up to 16 should be treated in adult wards and for those under 18 it should only happen where appropriate.
The follow-up study in partnership with the Young Minds charity, based on in-depth interviews with 16 young people and a survey of more than 200 NHS trusts, said progress was being made.
Half of respondents provided evidence that they were going to comply with many of the recommendations from the original report which ranged from meeting the target to providing specialist support to those in adult wards in the meantime.
But the report still revealed only 15% of trusts were currently treating all children on the right wards.
'Stare at the wall'
It found that in some cases young people had spent extended periods of up to a year on adult wards where their time was often unstructured.
It added that in many cases little attempt was made to help them continue with their education with some being left to "stare at the wall".
Sir Al said: "We cannot afford to ignore the current shortfall in the treatment and care of young people with mental health problems.
"Admitting these young people to inappropriate facilities at a time when they are at their most vulnerable is detrimental to improving their health."
Sarah Brennan, chief executive of Young Minds, added she hoped the report would act as a "spur" to improve care.
"The research reveals a bleak picture of the condition of mental health services for young people."
And Liberal Democrat health spokesman Norman Lamb said: "It is a scandal that children are being treated on adult mental health wards in so many places."
But a Department of Health spokesman said an extra £1.2bn had been pumped into mental health services as part of the rise in the overall NHS budget.
He said this had allowed the health service "to invest in the services and staff needed to transform mental health provision".
And he added ministers were confident the 2010 target would be hit.