The boy, who has not been named for legal reasons, handed himself into police on Monday after the incident outside the Collège Voltaire in Florensac in the south of the country.

The girl, who had been in dispute with a classmate over a relationship with a boy, died after a punch to her chin caused a haemorrhage and cardiac arrest. The accused boy had been training as a boxer for two years.

Local newspaper Midi Libre reported his mother saying “I know my son, and seeing his sister traumatised by what was happening at school made him want to protect her. He’s not a murderer. He’s never even hurt a fly. It’s a terrible accident and perhaps he wasn’t aware of his strength.”

She was careful not to excuse his actions. “I don’t think what he did was right and I’m not trying to excuse him. I’m his mother and as soon as he told me what had happened I took him immediately to the police in Agde.”

The father of the dead girl also spoke to the media. He said “this person has ruined our lives. When my wife caught up with him in front of the school he was saying “who wants some? Who can I hit?”. He had a look of pride and contempt. He even said to my daughter’s friend “next time, it’s you”. She was so frightened that she hid for the rest of the day.”

The prosecutor of the case, Patrick Mathé, told Midi Libre that the boy was distraught. “He broke down in tears several times when he realised the impact of what he’d done”.

The funeral of the young girl will be held this afternoon in Florensac. A silent march will be held in her honour on Saturday.