Nine out of 10 youths assessed at Western Australia's Banksia Hill juvenile detention centre had at least one form of severe brain impairment that is more likely to lead to problems with the law, ground-breaking research has found.

The Telethon Kids Institute study, published today in the medical journal BMJ Open, is also the first to assess the prevalence of foetal alcohol spectrum disorder (FASD), caused by prenatal exposure to alcohol, among youths in custody in Australia.

Key findings 89 per cent of Banksia Hill inmates have at least one form of severe brain impairment (severe neurodevelopmental impairment)

89 per cent of Banksia Hill inmates have at least one form of severe brain impairment (severe neurodevelopmental impairment) 65 per cent had at least three forms of severe brain impairment

65 per cent had at least three forms of severe brain impairment 23 per cent had five or more forms of severe brain impairment

23 per cent had five or more forms of severe brain impairment As previously reported in preliminary results last year, more than a third (36 per cent) have foetal alcohol spectrum disorder (FASD)

For most of the young people in Banksia Hill, it was the first time they had received a comprehensive assessment, despite many previously being in contact with child protection services and the justice system.

"These are missed opportunities for earlier diagnosis and intervention, which may have prevented or mitigated their involvement with justice services," the report found.

"We've failed these young people actually, society's failed these young people," lead researcher professor Carol Bower said.

High prevalence of FASD, other impairments

Following the recommendations of the Royal Commission into the Protection and Detention of Children in the Northern Terrirtory, researchers said their study provided evidence to further change the way troubled youths were dealt with in courts and in detention.

It has long been suspected many detainees at Banksia Hill suffer from Foetal Alcohol Spectrum Disorder. ( ABC News: Gavin Johns )

Of the 99 young people aged between 10-17 years who received a full assessment, almost all were male and 74 per cent were Aboriginal.

Signs and symptoms of FASD Low birth weight, major organ damage

Low birth weight, major organ damage Small head circumference, small eyes, thin upper lip and diminished groove between nose and upper lip

Small head circumference, small eyes, thin upper lip and diminished groove between nose and upper lip Failure to thrive, feeding problems, sensitivity to noise, touch and/or light and developmental delays

Failure to thrive, feeding problems, sensitivity to noise, touch and/or light and developmental delays Learning difficulties, memory problems, difficulties with social relationships, impulsiveness

As revealed in preliminary results last year, 36 per cent of the youths had FASD. It is the highest reported prevalence of FASD in a youth custodial centre world-wide, and almost twice as high as the rate identified in a study of children in Western Australia's Fitzroy Valley.

The final report has now found overall 89 per cent of the youths assessed had at least one form of severe neurodevelopmental impairment, whether it involved FASD or another impairment.

Sixty-five per cent had at least three forms of severe neurodevelopmental impairment, and 23 per cent had five or more.

The study found 89 per cent of youths assessed had at least one form of severe neurodevelopmental impairment. ( ABC News: Manny Tesconi )

These impairments cause problems with memory, cognition, motor skills, social skills, attention and executive function, such as not being able to relate cause and effect or plan things.

"Impairment in domains such as language, executive function, memory and cognition, may contribute to offending behaviours and/or difficulties in negotiating all aspects of the justice system," the report stated.

Twenty-four of the young people were also assessed to have an IQ score of less than or equal to 70.

Behaviour caused by injury, not choice

Professor Bower said the rates of severe brain impairment identified were enormous and should act as a catalyst to improve the way health, education, justice, child protection and other agencies managed troubled young people with behavioural difficulties, mental health problems and issues at school.

"What this study does is gives us evidence to inform system change for better outcomes for the young person and their communities," Professor Bower said.

"There's no reason to think there isn't a similar situation across Australia in the justice system."

Lead researchers Professor Carol Bower (L) and Dr Raewyn Mutch want young people to receive comprehensive assessments when they enter the juvenile justice system. ( ABC News: Nicolas Perpitch )

Paediatrician and researcher Raewyn Mutch, who conducted many of the assessments, said many of the youths now diagnosed with a severe impairment had been written off as simply bad kids but there was more to it.

"Your difficult behaviour comes from an underlying organic brain injury, it's not wilful. It's behaviour by accident of how your brain works, not by your wilful choice," Dr Mutch said.

The researchers have recommended young people be fully assessed when they enter the juvenile justice system, and if possible much earlier so plans can be put in place to help them and reduce the likelihood of jail.

"Our study provides strong science to support spending the money differently, so these young people can be rehabilitated as early as possible and that diminishes the other costs, such as grief and loss, whether you are the victim or the one who carried out the crime," Dr Mutch said.

Government to utilise study findings

The research was conducted with the support of the WA Department of Justice and the Department of Communities.

The justice department said it had worked with the researchers on new training programs starting today for staff to better recognise and help young people with neurodevelopmental impairments.

Corrective Services Minister Fran Logan said staff had previously recognised the symptoms which led some youths at Banksia Hill to engage in aggressive behaviour, rioting and an unwillingness to cooperate.

The study assessed nearly 100 youths aged between 10-17 years old at Perth's Banksia Hill Detention Centre. ( ABC News: Gavin Johns )

"But what [staff] didn't, I think, understand was that behind those problems were neurodevelopmental issues, that there were issues that could be defined as disabilities — neurodevelopmental disabilities — that will last with some of these kids for the rest of their lives," Mr Logan said.

He added the research would help staff create specific rehabilitation plans for the young detainees.

Mr Logan said the Government intended to push the findings of the study through its agencies to identify brain impairments among troubled youths earlier and help them.