Government-commissioned research has found that difficult children expelled from pupil referral units (PRUs) or special schools are being failed by the system designed to keep them in education.
The study is critical of support for excluded teens - almost all of whom have "extreme" special needs - and their families and called for changes to the procedures for helping them when they are barred from PRUs or special schools.
Academics spent two years talking to young people, their teachers and parents and found widespread problems, including "service providers" not knowing individual pupils, difficulties in finding them a place to study and in recruiting trained and experienced staff.
Official figures show pupils with special educational needs are eight times more likely to be excluded.
The vast majority of excluded pupils with SEN are "hard to place", and the study's authors, from the universities of the West of Scotland, Edinburgh and Warwick, say this is putting pressure on local authorities, which have to find alternative provision within six days of leaving school.
Long periods without learning exacerbates their problems, as does a target-led approach to catering for those excluded, they said.
One local authority worker, when asked by the researchers if he had actually met one of his charges, said: "No, I haven't; I've met the standard", and others echoed this view.
Ofsted has found many local authorities are having difficulty meeting the six-day rule, the target to get all children back in education within a week.
Some councils told the study it felt as if the Government had "thrown down the gauntlet", but delays in communication made it difficult to meet the target.
Most of the young people in the study lived in families where there were disruptions or difficulties, as well as the absence of a father figure.
The majority show poor attendance and had been given repeated fixed-term or permanent exclusions before, attending a large number of schools. Sending pupils to inappropriate places and the fact they had special needs were responsible for problematic behaviour.
"The catalyst for a young person's permanent exclusion was generally a violent assault on a member of staff," the study said.
"Persistent disruptive behaviour, often involving systematic bullying of younger children, instances of physical assault and damage to property were contributing factors.
"Exclusion was viewed by staff as a last resort, and as the only means of regaining control of an extremely difficult environment. Schools and families appeared to have limited capacity to mitigate the impact of the exclusion, or to plan alternatives."
Those with a history of violent, and multiple and complex behaviour were the hardest to place in other schools, the researchers found, and this put a strain on families already perceived as troubled.
The use of private tuition for six hours a week is a common interim arrangement.
Other issues included the waiting time for mental health referrals and lack of collaboration between education and social workers.