A teenage lacrosse star killed himself after he was summoned to court for possessing cannabis worth 50p, an inquest heard.
Ex-head boy Edward Thornber was found hanged on September 15, 2011, after being caught smoking the drug in Cornwall.
Two days earlier, the Didsbury 17-year-old had received an order to appear in court - but a law firm acting on behalf of his family say the teenager should have only been given a warning.
A student at Loreto College in Hulme, Edward had been head boy at The Barlow RC High School in Didsbury and was hoping to coach lacrosse in America before going to university.
However, he had been caught smoking cannabis with a friend earlier that summer while on holiday in Newquay.
It was the second time he had been caught with the drug.
At the town's police station, he agreed to accept a "final warning", which he believed would not result in him having a criminal record - or jeopardise his chances of pursuing a lacrosse career in the US.
However, his family's solicitor at law firm Pannone LLP says Devon and Cornwall Police made a series of errors following his arrest.
Among them included the details of Edward's case being put in a blue file instead of a pink youth file - resulting in the matter being processed wrongly and a court summons issued.
A spokesman for Pannone said: "All in all there were at least seven opportunities to spot and rectify the error that were missed.
"An internal report by the force has recommended a number of significant changes to procedures."
It is thought on the day Edward died, he first went to Manchester city centre before heading to Didsbury park, where he hanged himself.
His body was discovered by a jogger.
According to reports, a note to his parents, the summons notice and the court notice were found near his body.
Manchester coroner Nigel Meadows, who recorded a verdict of suicide at Edward's inquest on Friday, did not link the police errors directly with the youngster's death.
However, he acknowledged that Devon and Cornwall Police had since introduced procedural changes as a direct result of Edward's case.
Mr Meadows has also since written a letter to the Home Office alerting them to the potential dangers in issuing youth summons.
Edward's parents, Ann and Adrian Thornber, say they have been devastated by their loss, but were grateful their son's inquest looked in to the reasons why errors occurred in the handling of his case.
Mrs Thornber, who told the hearing neither she nor her husband knew about their son's summons, said: "We want to ensure the failings in procedure that we believe ultimately led to our son's death do not happen again and lead to another tragedy."
Have you been affected by issues in this article? In the United Kingdom, call the Samaritans on 08457 90 90 90.Suggest a correction