The attacks happened in the playground of the school

On Tuesday, the 14 year old was sentenced to four months detention and training after the attack on two teachers at the school in Cardiff which cannot be identified for legal reasons.

At a hearing at Cardiff Youth Court, the teenager - not identified because of his age - admitted actual bodily harm, assault and harassment.

The court heard that he had been permanently excluded from the school and had returned to see his friends - on being told to leave he attacked two teachers.

Women members of staff were so frightened that they locked the doors of classrooms Alex Dubljvic, prosecuting

Mr The court was told how the boy had been in trouble at school several times before the attack.

Alex Dubljvic, prosecuting, said: "He was a major problem causing major disruption at the school.

"He was abusive to staff, was involved in fights with other pupils, was caught smoking, did not go to lessons and was making hoax calls."

Such was his reputation, the court was told, that on spotting the boy in school grounds, female members of staff were "so frightened that they locked the doors of classrooms".

During the subsequent altercation, the teenager punched a male teacher and knocked a woman teacher unconscious with a single blow.

The female teacher told police the boy had clenched his fists "like a boxer".

The grandmother was responsible for his up-bringing and her death was the catalyst which started these offences Defender, Geraint Richards

She said: "He had an evil look on his face and was ranting.

"I turned away to get help then felt a big thud to the side of my face.

"I felt my brain rattling around inside my head. The next thing I remember is lying on the floor."

'Persistent offender'

The court heard how the teacher, who had been taken to hospital with a suspected broken jaw, had recovered but suffered flashbacks three months after the attack.

Sentencing the boy, youth court chairman Lenna Pritchard-Jones said: "We feel the offences are very serious because of the nature and extent of the harassment and violence towards the victims.

"You are a persistent offender and a serious danger to the public."

His solicitor, Geraint Richards, said the boy was "well-balanced and well-mannered" until the death of his grandmother three years before when he began distancing himself from the rest of his family.

The boy's parents, he added, were law-abiding people who are mystified by his behaviour and on one occasion the boy's own father had reported him to the police.

He said the family now plan to make a fresh start and move out of the Cardiff area.