Tashaûn Aird, 15, died after being knifed nine times in the chest, neck and back on May 1 2019, when his attackers wrongly identified him as being a member of a rival gang.
His heartbroken mother received her son’s letter of acceptance to a creative arts college after his murder, for which a 16-year-old boy was jailed for life earlier this year.
Romaine Williams-Reid, 19, and a boy aged 16 were also convicted of manslaughter and jailed for 12 years.
Tashaûn was expelled from school in July 2017 for allegedly damaging a teacher's property, the report commissioned by City and Hackney Safeguarding Children Partnership found.
He had already been temporarily excluded for the incident and was "responding positively to the sanction", it states.
However, the school decided to permanently exclude Tashaûn and he was placed in a Pupil Referral Unit and then an alternative education provider.
The council found the expulsion was unlawful but governors refused to reverse the decision.
The exclusion was "a catalyst" to the deterioration in Tashaûn's behaviour and independent reviewer Charlie Spencer said and it "exposed [Tashaûn] to a new, more challenging environment that he realistically did not need".
“As a consequence, [he] was subsequently educated with a cohort of other excluded pupils who had displayed more entrenched behavioural issues, complex needs linked to special educational needs, significant safeguarding needs and issues relating to gangs, criminality and anti-social behaviour," the report states.
“It is the view of the lead reviewer that the school failed to exhaust all available opportunities to maintain Tashaûn at his secondary school.
“Several serious concerns about the permanent exclusion were noted by Hackney Learning Trust, which were all ignored by the school. The school governors had a duty to re-consider their decision, which they did and upheld, despite the permanent exclusion being judged to be unlawful.
"It appeared that the school was determined to permanent exclude, without consideration of the wider implications to his safety, well-being or his education."
Three months before his murder Tashaûn was seriously injured in a stabbing attack when a teacher at the pupil referral unit let him attend a youth club unsupervised.
After surgery he told a social worker he that “he was afraid and feared for his safety”.
Police noted he was “going missing and local intelligence suggested he was being criminally exploited and possibly involved in county lines”.
However, there was no evidence to suggest he was a member of a gang.
Charities have warned about the alarming rise in children permanently excluded from school being linked to the soaring numbers recruited into county lines drug-dealing, as well as youth violence and imprisonment.
Ministry of Justice data suggests expulsion is the biggest single common factor among boys ending up in prison.
Hackney New School, which Tashaûn was expelled from, was rated as "inadequate" by Ofsted last year and has now been taken over by the Community Schools Trust, which runs two outstanding schools in Newham.
New headteacher Charlotte Whelan said: "The death of Tashaûn is a great tragedy. My condolences and sympathies are with his family.
“Because his exclusion from this school took place prior to my becoming headteacher I cannot comment directly on the findings of the report.
“Indeed, none of the governance or leadership team who oversaw Tashaûn case are now at the school.
“Had our highly experienced team been in charge when Tashaûn was at the school this case would have been handled adhering strictly to professional guidelines."
The school’s former governor and founder, Andreas Wesemann, said: “We spent a lot of time considering the implications for Tashaun’s prospects, and I wish we had been able to find a way of re-integrating him into school.
“As you know, subsequent events at Hackney New School showed that the school was performing well below expectations in many respects – including, to be clear, well below our expectations as founders of the school.
"Ultimately the board of governors was responsible for this. Today, I am glad to say, Hackney New School is in much better hands.”