Hatchet plot to stop girl dating mate

A model high school student has been sentenced to eight years in jail in Tasmania for the attempted murder of his classmate's ex-girlfriend.

The 15-year-old Hobart boy, who excelled in class and on the sporting field, packed two hatchets in a backpack in preparation for the meeting he organised with the 15-year-old girl in March.

At the remote location beside the Derwent River, at 3pm on a Sunday, he asked her if anyone would miss her if she were dead, Supreme Court Chief Justice Ewan Crawford said in sentencing today.

Upset and depressed about having been dumped two weeks earlier by the intelligent and popular boy's friend, she said she doubted anyone would and the boy became angry.

"He then removed one of the hatchets from his backpack and struck her with it in the back of her head, intending to kill her," Justice Crawford told the court.

The court was told the boy did not like the girl and he had made that clear to others before the attack.

"He did not want his friend to go out with her," Justice Crawford said.

She was discovered sitting dazed on a park bench at her Hobart school 22 hours after being left for dead by the boy.

He also stole her mobile phone, which he later showed as part of a boast to his friend, her ex-boyfriend, and another classmate after the attack.

Police soon after arrested and charged the boy with attempted murder, to which he eventually pleaded guilty.

Despite his two friends' evidence, the boy denied the crime until investigators showed him telephone records linking him to meeting the girl and her phone, which they found in his bag.

She now suffers brain damage, an aggressive change of personality and massive weight gain after nine blows to her skull with the hatchet kept her in hospital for three months.

She thought the boy was a friend and had enjoyed his company, the court was told.

"She misses very much going to school and having friends," Justice Crawford said.

The judge said the boy displays signs of narcissism, highlighted by a grandiose sense of superiority and a preoccupation with being a success.

He has a tendency towards being exploitative, a lack of empathy and mildly arrogant attitudes, Justice Crawford said.

He said he was a highly intelligent but immature boy who had shown only limited remorse but had no psychiatric illness.

The most recent psychiatric report reveals the boy had developed fantasies of grandeur and imagined himself as a "genius" who could commit a serious crime and avoid detection, Justice Crawford said.

"He is intelligent and received excellent high school reports," Justice Crawford said.

"His last in December 2008 said that he was a polite, friendly and co-operative student who was successful both academically and on the sporting field.

"His class teacher and grade supervisor referred to him as a very good student, popular and one who would help other people in trouble."

He will be eligible for parole in four years.

- AAP