Imre Doue was found guilty in July of murder, and Marko Balaz was convicted of manslaughter over the fatal stabbing of Daejaun Campbell following a six-week trial at the Old Bailey.
Doue, who was 17 when he committed the crime but has since turned 18 and can now be named, was sentenced to a minimum term of 21 years in prison.
Balaz, 19, from Abbey Wood in southeast London, was jailed for a minimum term of 11 years.
Daejaun cried out “I’m 15, don’t let me die” after he was ambushed in Woolwich on 22 September last year, the court heard.
He died from his injuries, which included two stab wounds and six superficial cuts.
Daejaun’s mother, Jodian Taylor, said his death could have been prevented had authorities listened to her concerns.
She believes her son, who she described as an “intelligent”, “fun” and “witty” teenager, was a victim of grooming.
“My biggest fear was to get that phone call that he was hurt. Instead, I am living my worst nightmare, that he is no longer here… he just died on the side of the road like a dog,” she said.
“The bit that hurts is that it could have been prevented, because the authorities were aware.”
The detectives investigating the unprovoked attack said a motive was never established, but they believe Daejaun could have been on Eglington Road that day because he was being exploited into selling drugs in the area.
Ms Taylor said this did not come as a surprise, because she had noticed a change in her son’s behaviour before his death.
She said Daejaun went from being a sweet, caring child who doted on his younger siblings to a secretive teenager who was anxious to be seen out and about with his family.
She feared for the worst, and her mother’s intuition told her that her son may be at risk.
Ms Taylor said she started monitoring Daejaun closely, she raised concerns to his school and even attempted to give up parental responsibility, hoping the local authorities would step in and save her son.
“I never thought I would have to make the call to ask for him to be removed. I never kept my son’s behaviour a secret,” she said.
If parents believe their child is at risk of criminal exploitation, the local authorities’ children’s social services have a duty to investigate the safeguarding concerns and provide support.
But Ms Taylor said her concerns were dismissed and she was told that her son “didn’t meet the threshold”.
She said she only received a response to her calls for help the day after her son was killed.
“The focus should be more around prevention,” she said.
“[When I] was asking for all the help to prevent what happened to my baby, that wasn’t given. But in his passing, I’ve had all these professionals coming to me now, offering me all the help. I am thinking, what’s the point now?”
Despite the convictions, she is not convinced that means justice has been served.
“The justice that they tell me I am going to get is not enough. Because the people who groomed him still get to live their [lives] as though everything is okay,” she said.
“They get to groom other people’s children to do their dirty work, and I get to sit here trying to figure out how I am going to live with this pain.”
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A spokesperson for the Royal Borough of Greenwich told Sky News that Daejaun’s death “stunned our borough”.
It added: “We can’t comment because there is an ongoing independent formal child safeguarding review by a multi-agency board which will examine the circumstances that led to his tragic death.
“Whenever something serious happens to a child in our care we have to review what happened and why, and what we did and how we handled it. That process is independent and involves Daejaun’s family – and expected to finish later this year.”
