Stephen died in hospital on Wednesday night from injuries he received in the fight after practice had finished.
He wasn't known to his family as a fighter but as "gentle, well mannered and respectful", said his aunt Dr Margaret Dudley.
"But apparently it was pre-arranged, like they do ... You know, there will be a fight after school ... so I've heard that was the situation."
If that was true, it came out of the blue for the family. "There is a culture in these schools that fighting is to be expected and is the norm ... It's part of a culture to have these organised fights after school," Dr Dudley said.
Fighting didn't fit the nature of the Stephen the family knew, she said.
"I think he was a little bit fearless. He was never a big rough kind of guy and that could have been his undoing."
Dr Dudley said family members were gathering to support Stephen's parents, Brent and Mona.
Her daughter Rachael Andrew said the phone call from Stephen's father to break the news was "haunting".
"He said to my mum that he (Stephen) was beaten to a pulp. It was a schoolyard fight that got out of control. I could hear his mother in the background and it was haunting the way she sounded. It was her eldest son; he was precious."
Ms Andrews said one of Stephen's cousins lived with her and also attended Kelston Boys. "He was just talking to Stephen after school and they were going to walk home together but Stephen stayed for rugby. By the time (the cousin) got home ... I already knew and told him. He couldn't understand. He said, 'But I just saw him'."
She said the family were devastated. "He was really good to his mother. He helped her a lot because they had young kids. He didn't mind doing the chores around the house. Most teenagers hate doing that sort of thing but he would always help."
Two boys, aged 15 and 17, appeared in court in Waitakere yesterday charged with assaulting Stephen.
Judge Brian Callahan suppressed all details that would identify them.
Defence lawyer John Munro said the youths would be taking time to collect their thoughts on what had happened.
"(They) are very upset for everything. They're just upset all round and they are taking some time to settle down and reflect on things."
It's understood the fight was supposed to be one-on-one but the second boy joined in and together they punched Stephen until he fell to the ground.
A witness told TV3: "There was just a bunch of boys having some fights up there ... I came back and he was on the ground, gone. So me and my mate gave him CPR. It was too late."
Detective Inspector Bruce Scott said a pathologist had completed a physical examination of Stephen's body but was still doing some toxicology work. He said he could not comment on the autopsy results.
Based on the evidence presented to police thus far, neither of the accused teenagers would be charged with murder, Mr Scott said.
"There are certain intents that you have to prove for a charge of murder and I don't believe in the circumstances as we know them at the moment that we would have those intents, or be able to prove those intents to the court."
It seemed like "a moment of madness, and they'll have to live with the consequences".
Mr Scott said police had received an "indication" from someone that a witness had filmed the assault on a cellphone, so the mobiles of several people had been collected.
"We've taken the cellphones with their permission to see what's in them. All the students police had spoken to were co-operative. They're all good kids."
He did not rule laying further charges against the two teenagers arrested, depending on the results of a post-mortem examination.
Stephen's body was released to the family late yesterday afternoon. His funeral service will be held on Tuesday at Kelston Intermediate School, where his father is a caretaker, before his burial in Waikumete Cemetery.
- Additional reporting: Morgan Tait and Edward Gay
