Mr W, who cannot be named for legal reasons, was given leave to apply on his son's behalf for a judicial review of the headteacher's decision not to take disciplinary action after the boy's arm was broken in the lunch queue.
Philip Engelman, who represented the family in court, argued that letters from the head and governors showed that the school had "closed its mind to this serious matter and the bullying that underlies it.
"There has not been a serious investigation of the underlying facts, or serious consideration of the harm actually inflicted on the applicant by other boy."
He said the head had made it clear soon after the incident that he did not believe there had been a serious assault. The boy, W, had received a spiral fracture in his arm which suggested that considerable force had been used.
His assailant had admitted: "I went and gave him a Chinese burn and he moved, then I heard it click."
A police investigation decided that the assailant might have been guilty of criminal assault but his parents, on legal advice, had refused to accept a formal caution. Police said there would be no prosecution.
In January, the governors decided that no action would be taken against the other boy over the "accident". They said they were satisfied with the school's anti-bullying policy.
The local education authority later wrote to Mr W saying that a police investigation had not found "evidence of intent" to cause harm and no further action was proposed.
When W returned to school he had been isolated from other pupils and had not been allowed to take part in activities outside lessons.
The chairman of the governors had written to the father saying that they would not tolerate a campaign against the good name of the school and its headteacher.
Mr Justice Forbes ruled that it was "an appropriate case" for a judicial review.
Outside court, Mr W said: "This was serious bullying which required serious action. My son is utterly shattered by what has happened. It is outrageous. On the one hand he has discovered the truth of British justice. A 10- year-old juvenile can do anything and doesn't get prosecuted and his parents are allowed to refuse a caution."Reuse content