Michael Uriely died five days after leaving the Royal Free Hospital in London in 2015.
In the months before his death he was seen by many doctors who failed to diagnose his condition was chronic.
Had he been given a high dose of steroids in hospital "it's unlikely he would have died", the coroner said.
Michael's parents took him to hospital following a violent coughing and vomiting episode on 18 August that left him struggling to breathe.
By 20:00 BST he was allowed to go home, but the inquest heard he suffered another attack  in the early hours and was taken back to A&E.
This time he was kept in overnight, but despite two internal investigations medics failed to diagnose his chronic asthma.
He was again released from hospital the following day and died from an acute attack on 25 August.
When Michael was admitted to hospital twice within 24 hours, "alarm bells should have begun to ring", Coroner Dr Shirley Radcliffe said.
She told Westminster Coroner's Court earlier a "totally inadequate" medical history was obtained on that occasion and no connection was made with his previous admission.
She added: "The opportunity was lost to recognise this as a serious problem - the history and signs were there to be seen and understood.
"But sadly it wasn't recognised and he was discharged essentially on the same treatment he had been on."
Following Michael's death, The Royal Free Hospital appointed two specialist respiratory clinicians, opened a dedicated asthma clinic and introduced a new strategy for dealing with children with asthma.
His parents, Ayelet and Roy Uriely, said Michael was "an extraordinary boy, both in personality and intelligence".
They said: "He doted on his younger twin sisters, who adored him, and always joined in with their games".
Michael was diagnosed with asthma when he was two and began learning chess aged three.
Since his death, seven other children in London have died from asthma, the inquest heard.
A nine-year-old chess champion who died of an asthma attack could probably have been saved if he had not been sent home from hospital, a coroner has ruled.