Schools and social services are failing to prevent youngsters ending up as criminals, ministers have been warned.
A report commissioned by the Scottish Executive said more should be invested in specialist support for teenagers when they start to go off the rails.
The Edinburgh University study confirmed that exclusion from school could be a stepping stone to a life of crime.
The executive says it was reviewing its guidance on exclusions.
The report says teenagers, especially boys, have a higher chance of a criminal conviction if they leave school as soon as they turn 16.
"Excluding vulnerable young people from school is not a decision that's taken lightly"
The researchers said there was an urgent need for investment to help schools hang on to troubled young people.
They would like to see small centres on site so that disruptive pupils could be taken out of class but not expelled.
Skilled staff in the centres would offer intense support and eventually integrate the pupils back into classes.
An executive spokesperson said ministers wanted to promote positive behaviour in schools.
"Excluding vulnerable young people from school is not a decision that's taken lightly.
"Many heads feel they have no option but to leave the pupils in class to continue to disrupt their classmates' education"
"We need to ensure that excluded pupils can still access the education they need, deserve and expect and we're reviewing guidance on exclusions accordingly."
Tory spokeswoman Liz Smith said it was important that there were enough dedicated units, or separate schools, for excluded pupils.
"If there are not enough of these facilities, head teachers are only too aware that badly-behaved pupils may cause mayhem in their local communities if they were to be excluded," she said.
"For this reason, many heads feel they have no option but to leave the pupils in class to continue to disrupt their classmates' education.
"The new executive must not see this as merely the lesser of two evils. Rather, it must act to give heads the confidence that excluded pupils can be dealt with properly."
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