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.
Levan Menzies was 17 when he was one of four killers jailed for 110 years between them in 2009 after being found guilty of the murder of 17-year-old Tarek Chaiboub the year before.
Nigel Junior Ramsey, his brother Denzil Ramsey, their next door neighbour Levan Menzies and pal Michael Chattoo were all involved in a plot to kill Tarek, who was hunted down and shot dead at a city barber’s on Spital Street, Burngreave.
They were all part of the S3 postcode gang operating in Burngreave and Pitsmoor at that time and wanted the teenager dead when rival factions in the gang clashed.
They blamed Tarek, of Castledine Gardens, Wincobank, for passing on information that led to the near-fatal stabbing of another S3 gang member.
Nigel Ramsey – known on the streets as ‘The General’ and formerly of Andover Street, Burngreave – was said to have been in charge of the younger members, and organised the killing while behind bars. Photo: SYP
Ruben Monero and Isaac Ramsey were both 17 when they involved in an attack which resulted in the death of 35-year-old Marcus Ramsay on August 8, 2020.
Marcus died after an unconnected altercation at a street party on Horninglow Road, Firth Park, escalated into significant disorder, which culminated in him being stabbed through the heart.
Moreno was convicted of murder after a trial, and Ramsey was found guilty of manslaughter.
Moreno was sentenced to serve a minimum of 18 years behind bars and Ramsay was jailed for a minimum of 14 years.
Both teens had turned up at the party armed with knives. Photo: SYP
Jabari Fanty was 19 when he was involved in a “planned and cold-blooded murder” in Sheffield'
Fanty, of Broadhead Road, Stocksbridge, and two others, were found guilty by a jury of murdering 20-year-old Ramey Salem at a flat on Grimesthorpe Road South, Burngreave, Sheffield, on November 16, 2020.
He was shot multiple times.
Stephen Wood QC, prosecuting, told Sheffield Crown Court the case involved drug dealing, guns and gangs and the ruthless lengths gangs will go to in order to protect their turf. Photo: SYP