The family of Yousef Makki will push for a judicial review to quash a coroner's inconclusive verdict into the teenager's fatal stabbing.
Senior South Manchester Coroner Alison Mutch said she could not safely conclude the death was either unlawful or accidental, instead recording a narrative verdict following a seven-day inquest in November.
Yousef's family described the conclusion as 'disgusting' at the time.
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Now a QC acting for Yousef's father Ghaleb Makki will apply to the High Court for a judicial review to quash the coroner's ruling and seek a new inquest in front of a different coroner.
Yousef, a talented bursary student at the elite Manchester Grammar School from Burnage, was just 17 when he was fatally stabbed through the heart by his friend Joshua Molnar, a former public schoolboy from a wealthy Hale family, during a confrontation in Hale Barns on March 2, 2019.
A jury acquitted Molnar, now 20, of murder and manslaughter later that year, although he was handed a 16-month detention and training order after admitting possessing the knife which inflicted the fatal injury and lying to police at the scene.
He says he acted in self-defence, alleging Yousef pushed and punched him and called him 'p*ssy'.
His co-defendant at the 2019 trial Adam Chowdhary, also 17 at the time but now 19, from Hale Barns, who described Yousef as his 'best friend' at MGS, was acquitted of perverting the course of justice.
He was given a four-month detention order after admitting possession of a flick knife, one of two he claimed he and Yousef had jointly ordered during a break from lessons at MGS.
Following November's inquest, Senior South Manchester Coroner Ms Mutch recorded a narrative conclusion, saying: "Yousef died from complications of a stab wound to chest. The precise circumstances in which he was wounded cannot, on balance of probabilities, be ascertained."
The family's formal application for a judicial review, written by Pete Weatherby QC who represented them at the inquest, argues the coroner's ruling was 'unreasonable' as it 'failed to address or make findings on central matters in the case such as to enable her to reach a conclusion - on the balance of probabilities - as to the lawfulness of the killing'.
The QC said the coroner 'failed to address or offer any analysis' about Joshua Molnar's credibility, state of mind at the time of the stabbing or whether he produced a knife before Yousef, or whether Yousef had drawn a knife at all.
The application was due to be formally lodged at the High Court today.
Yousef's sister, Jade Akoum, told the M.E.N : "We're really pleased that Yousef's dad is challenging the coroner's decision in court, and fully support him doing so.
"We hope that this legal action succeeds so that there can be a fresh inquest before a different coroner. This is the least that we owe to my mum, and to Yousef.
"We have known for a long time that getting answers for him wouldn't come easily, but we're not going anywhere, and will keep fighting for as long and as hard as it takes to get answers for Yousef."
