A jury ruled the death of 15-year-old Gareth Myatt, of Stoke-on-Trent, at the Rainsbrook Secure Training Centre in Northamptonshire, was accidental.
But jurors criticised civil servants at the Youth Justice Board (YJB).
They said the YJB's failure to review the medical safety of the system of restraints was a factor in the death.
Gareth was the first child to die while being restrained in custody.
He was held down by two male officers and a female colleague using the Home Office-approved seated double embrace restraint.
Gareth died in April 2004 from "positional asphyxia" after choking on his own vomit as he was held down.
The hold used to restrain him has since been banned by the Home Office.
Gareth had served just three days of a 12-month sentence at the centre near Daventry when he died.
The system of restraints was introduced in 1998 with a promise that its use would be constantly reviewed.
Despite numerous warnings about its safety, a medical review into the use of restraints was not ordered until after his death.
David Tuck, the Youth Justice Board's monitor - said to be the "eyes and ears of the Home Office" - wrote of his concerns about health effects of the techniques used by guards at the privately-run prisons, and at Rainsbrook in particular.
'Difficult to breathe'
In a letter written to managers in June 2002, Mr Tuck warned of the dangers of youngsters vomiting while being restrained.
One girl at the centre, known by the initial "C", complained she struggled to breathe while being held down.
More than a year later he wrote again, saying children were complaining their heads were being pushed down into their groins, doubling them up and cutting off air supplies.
In his first letter - which was sent to social services, Rainsbrook's director John Parker and head of care Barbara Davies, as well as the Youth Justice Board - Mr Tuck wrote: "C says she is accustomed to physical restraints from her other placements but none has been as uncomfortable as those applied to her at Rainsbrook.
"She says that the approved technique of bending her forward, placing her head between her knees, makes it difficult for her to breathe."
Nothing was done in the light of the letter, the inquest heard.
Speaking after the inquest, Gareth's mother Pamela Wilton Myatt's was critical of everyone involved in the detention of her son.
"It has been hard enough to accept what happened to Gaz," said Miss Wilton.
"But hearing everything that's come out... how long the injuries were going on, years of injury and vomiting and kids complaining.
"I hope to see change to ensure that it doesn't happen again, that kids are hurt."
She added that she was considering pushing for a criminal prosecution in relation to the death.
Deborah Coles, co-director of justice group Inquest, said: "The jury's verdict is a shameful indictment of a catalogue of failure by the Youth Justice Board.
"The jury accept that these failures directly caused Gareth's death. He died a most horrific and violent death while being restrained by custody officers.
"His death was entirely preventable and was a disaster waiting to happen."
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