The 16-year-old stabbed Mr Sumner with a knife in what was said to have been a revenge attack over an earlier incident, with Mr Sumner having been accused of smashing some windows.
He has not yet been sentenced but faces a mandatory life sentence when he appears at Sheffield Crown Court on Friday.
The killer is not the only teen to have been sentenced in Sheffield for murder and manslaughter over recent years.
Here are some other cases which shocked the city.
A 16-year-old boy, who cannot be named for legal reasons, stabbed 42-year-old Anthony Sumner in an attack in Windy House Lane, Manor, in July last year, in what is said to have been a revenge attack. Photo: National World
A 15-year-old, who cannot be named for legal reasons, was jailed for two years and eight months in October 2018 after admitting manslaughter.
He stabbed 15-year-old Sam Baker in Lowedges in the May of that year.
He handed himself in and told police that during an altercation with Sam, a blade Sam had been carrying himself was used against him. Photo: National World
Emar Wiley was just 16 when he stabbed a young dad-of-one to death in Sheffield in July 2019.
He received a life sentence for killing Lewis Bagshaw and was initially sent to Wetherby Young Offender Institute in West Yorkshire.
But just two months after being sentenced and ordered to spend a least 16 years behind bars, he stabbed a prison officer.
Wiley, formerly of Mason Lathe Road, Shiregreen, had extra time added onto his sentence.
Wiley stabbed Lewis twice in his chest in an attack on Piper Crescent. Lewis collapsed and died a short time later.
Wiley had attacked Lewis’ dad two months earlier and left him with a fractured skull. When Wiley and Lewis’ paths crossed, there was a confrontation and violence flared. Wiley chased Lewis and plunged a knife into him. Photo: SYP
In March 2018, Shea Heeley, aged 19, of Doe Quarry Lane, Dinnington, was jailed for life and ordered to serve a minimum of 24 and a half years for murdering Dinnington schoolgirl, Leonne Weeks, in January 2017. Photo: SYP