The child was subjected to the horrific ordeal within the grounds of her primary school by 23 classmates her own age for months.
An official inquiry into the abuse the child regularly suffered accepted that sexually harmful behaviour did take place.
But it concluded that no action could be taken against those responsible because they were too young. The youth of the children made it impossible to gather proof of what had happened and all were under the age of criminality.
The conclusions of the serious case review were published two years after the allegations were first made. A review of that inquiry process itself is now under way.
.The unnamed schoolgirl is from Wales but neither the school she attended nor the local authority can be identified. The child has since been moved to a new school but her mother claims she will be scarred for life by the abuse she suffered.
Keith Towler, Children's Commissioner for Wales, called the review "a shocking failure". He said that "the bottom line is the family will never know what happened to their child". He also acknowledged that the serious case review system was "failing some of the most vulnerable children".
The mother of the child said it is wrong that nobody will be held accountable for what happened. The serious case review was only launched by the local authority when she took legal action. The girl's mother has spoken of her shock and horror at learning from her daughter about the abuse she suffered.
In an interview with BBC Wales, she said: "She was telling me things that I think every mother dreads to hear from their daughter. It was horrendous what she'd gone through. Every day she was being stripped. Every day she was being sexually and physically abused and every day she cried out for help and nobody ever came."
Mr Towler said a review of the serious case review system was now under way. He said: "Clearly there are issues with the serious case review system and there is consensus that the current serious case review arrangements are not working effectively."