Marcus James Pollard, 63, abused the 15-year-old girl at Rose Bay High School, where he worked, and his home in the late 1990s.

Over a period spanning months, he would kiss and touch her in the school's photography room up to two-or-three times a week.

He also met the girl at the school in the 1998 summer holidays, drove her in his ute to his home and abused her.

"There was a sustained course of sexual abuse over several months involving an appalling breach of trust and months of slow grooming," Justice Alan Blow said during sentencing in Hobart Supreme Court on Tuesday.

Pollard, who earlier pleaded guilty to one count of persistent sexual abuse of a young person, was jailed for three years with a non-parole period of 18 months.

He collapsed in the dock after the sentence was read out.

Justice Blow said Pollard had serious psychological problems when he offended, was lonely, unhappy with work and suffering badly from depression.

The judge accepted Pollard's friendship with the girl, not just his sexual activities, was meeting an emotional need and his judgment "was clouded" as a result.

"I accept he would not have offended but for the state of his mental health during the months in question," Justice Blow told the court.

One of the first instances of abuse occurred when Pollard kissed the girl on the lips in his office after months of close contact where he would brush up against her.

Pollard further abused the girl on a school camp, kissing her in his tent while wearing only underwear.

He lost his job at the school after the girl raised abuse allegations in 2000 with the state education department.

"It is clear that Pollard's abuse has caused terrible psychological suffering over many years," Justice Blow said.

"The complainant feared Mr Pollard would interfere with her marks and thus her future career."

Australian Associated Press