A PRIMARY school teacher with 25 years' experience was yesterday jailed in the High Court for having sex with a 13-year-old pupil. Mr Justice Duffy found the man, who cannot be named to protect the girl's identity, guilty of two counts of unlawful sexual intercourse and sentenced him to three years and eight months in prison. The teacher, who was the girl's form master and married with three children, had committed a terrible breach of trust, said the judge. The defendant was a figure of authority to the girl and what he had done to her amounted to rape, the judge said. He placed great emphasis on the fact that by pleading guilty to the offences, he had saved the girl from the trauma of giving evidence. Counsel for the 49-year-old teacher, a Christian, had described the case as one of ''fatal attraction''. The defendant had pleaded guilty to two counts of unlawful sexual intercourse, one when the girl was 13 in 1991 and one when she was 14 in 1992. He faced another two counts of unlawful sex, one when the victim was 11, and one count of indecent assault, but the Crown had offered no evidence. Prosecuting counsel Paul Madigan told the court the defendant was the girl's form master when she was in primary five and six at the Kowloon government school from 1989 to 1991. They became friendly in December 1989 and had first had intercourse later that month at his home. Thereafter, they had sex about twice a month. In September the following year, the defendant persuaded the girl's mother to let her daughter take private lessons at his home each Sunday. The offences came to light when police went to the teacher's home on March 1, 1992, in response to an anonymous complaint. The girl admitted that sexual intercourse had taken place that day and that they had watched sex videos. Counsel for the defendant Robert Buchanan told the court his client was brought up in a religious environment, his father being a missionary and his brother a priest. Both he and his family were devout Christians and prior to the offence, he was a respectable and popular teacher. However, said counsel, because of the conviction, he would have to leave teaching and stood to lose about $500,000 in a provident fund. At one stage, he said, due to financial difficulty, he gave private tuition to a group of students and the girl was among them. In the beginning, he said, the man treated her like everyone else although she clearly had certain feelings towards him. ''Whether intentionally or not, the girl, through her admiration and expression of affection for the defendant, lit the fuse of what I can only describe as fatal attraction,'' he said. Mr Buchanan said this case was devastating to the teacher's life and it had brought shame and humiliation upon him. His children had forgiven him and were standing behind him, said Mr Buchanan.