An eight-year-old boy would have had more chance of surviving a fatal asthma attack but for an error by an ambulance call-handler, a coroner has ruled.
Clayton Barker died after paramedics were delayed because his grandmother's 999 call was wrongly categorised as less serious than it was, the inquest into his death heard.
If the "correct response" had been taken, the ambulance would have arrived before Clayton collapsed and his chances of survival would probably have been "enhanced", Simon Nelson, senior coroner for Manchester North, said.
Mr Nelson, giving his ruling at the end of the inquest in Heywood, Greater Manchester, said: "Clayton Barker died following an acute asthmatic attack.
"The evidence at the inquest confirmed that the first of two emergency 999 calls was not processed in line with best practise.
"Had the correct response been generated, then the ambulance would have arrived before rather than after Clayton collapsed, in which case, on the balance of probabilities, his chances of survival would have been enhanced."
Gemma Barker described her son, one of three brothers, as "mischievous" and "full of energy", despite being diagnosed with asthma from the age of five.
Clayton, from Oldham, Greater Manchester, started struggling for breath while enjoying a sleepover at his grandmother's house on March 14 last year, the inquest heard.
But when his grandmother Elaine Barker phoned 999, the operator thought the emergency was less serious than it was so the next waiting ambulance was sent to another emergency instead - and Clayton was not reached by paramedics until 23 minutes after the initial call.
During the hearing it emerged the call operator - who had taken nearly 80 calls during the "extremely busy" 12-hour shift - asked Clayton's grandmother: "Is he having any difficulty speaking through breaths?"
But she wrongly registered the answer as "no" instead of "yes".
It meant the situation was thought to be less urgent than it was and the call coded green instead of red, for potentially life-threatening.
Elaine Barker had phoned 999 at 7.17pm and an ambulance dispatched at 7.29pm, arriving at 7.40pm.
If the call handler had written down "Yes" an ambulance could have been sent from a much closer station and been mobile at 7.21pm and on the scene at 7.27pm.
It meant the ambulance could have been there five minutes before Clayton collapsed at 7.32pm, but instead the first ambulance arrived eight minutes afterwards.
Clayton was eventually taken to the Royal Oldham Hospital by ambulance staff, but was pronounced dead on arrival shortly after 8pm.
Angela Lee, assistant service manager at the emergency centre of North West Ambulance Service (NWAS) told the inquest the call handler had been using a series of scripted questions as part of a "medical priority dispatch system" that was used nationally and internationally.
Mrs Lee said all staff had been reminded of the importance of recording information accurately.
She added: "It was an individual error, I don't believe there needs to be a change in procedure."
Gemma Barker is understood to be taking legal action against NWAS through criminal negligence lawyers at Slater & Gordon.
Solicitor Zak Golombeck said: "Gemma and her family would like to thank the coroner for his full and thorough investigation.
"The evidence was unambiguous that had the initial 999 call been categorised correctly and attended Clayton in a timely manner, Clayton's chance of survival would have been enhanced.
"Gemma's loss is not something words can describe.
"Clayton was a happy and lively young boy who will be deeply missed by his family, especially his two brothers.
"I will now be advising Gemma in relation to pursuing legal action against the ambulance service."
Derek Cartwright, director of operations for NWAS, said: "The Trust would like to offer our apologies and express our sincere condolences to Clayton's family. We fully appreciate that this must be a very difficult time for them.
"The control manager informed the court that an error had been made in the control room at the time of the incident, which unfortunately resulted in a delay in despatching an ambulance to the address.
"We therefore accept the coroner's comments and since this tragic incident, have reviewed our processes within our control rooms.
"The trust is committed to learning from all incidents in order to avoid any similar occurrences and to improve patient care and safety.
"We would also like to thank the coroner for his handling of this sensitive case."