A primary school head teacher, who duped pupils into taking part in what he said was a survey for a tv sex education programme and then sexually abused them, was jailed yesterday for seven years.

John Forsyth singled out the girls, aged 10, 11 and 12, and told one he loved her, abused her on his daughter's bed, and established a code with her so she would know if his wife was out and she should visit. He told the 11-year-old he wanted to make love to her.

His offences came to light only last year, after almost 20 years, when one of the victims discovered that a friend's children were about to attend the school where he was then teaching.

She contacted another friend whom she believed might have been a victim, spoke about the trauma for the first time, and the offences were revealed.

Police interviewed other former pupils, and yesterday Forsyth, 50, appeared at the High Court in Aberdeen.

He pled guilty to seven charges of abusing seven girls at Tullos Primary School, at school playing fields, and in his home at Braemar Place. Pleas of not guilty to five other charges were accepted.

Passing sentence, Lord Philip told Forsyth: ''You have pled guilty to seven charges of the utmost gravity, involving repeated conduct over a considerable period of time against children entrusted to your care and guidance. You abused that trust and inflicted damage which has affected the rest of their lives.''

Advocate Depute Graham Bell, QC, said the offences had taken place from 1977-1980 when Forsyth was assistant head teacher of Tullos and had his own room with an en suite bathroom, where most of the offences took place.

''The witnesses speak about him having been a good teacher although a strict disciplinarian, and all speak to his interest in their sexual development,'' he said.

''He watched TV sex education programmes with the children and then used the connection as an excuse to carry out what were described by him as a survey of their body measurements.''

As this was described, two of his victims left the court in tears.

The Advocate Depute told how Forsyth was also involved in volleyball and cross-country coaching. He told one girl he would give her relaxation exercises and massaged her shoulders, breasts and the inside of her thighs.

Forsyth approached one 11-year-old and told her he had ''special feelings for her which he had not felt for anyone except a former pupil at the school''. He called her to his office and then sexually abused her. ''He told her he loved her and she, at that age, submitted to this conduct and at the time felt somewhat flattered she had been selected by him.

''This continued outwith the school and he would walk home with her after school, and often he held her hand in public and kissed her in public.

''He asked her to visit him at his home and adopted a code, telling her he would leave the curtains open if his wife was in and close them if she was out, and she would then know whether she should call at the house.

''On occasions when she did call at the house he would take her to his daughter's bedroom, where he lay on the bed with her. He spoke of them one day making love and indicated he would like to engage in sexual intercourse.''

Mr Bell said that at the time the victims felt they were someone special to the assistant head teacher. ''He clearly exerted considerable influence over them. As a result they did not, at that time, compare experiences with one another.''

The victims had all been deeply affected in later life by his conduct, and by having to recount the incidents almost 20 years later.

Mr Murdo McLeod, for Forsyth, said his client had been a ''well respected and popular teacher'' and the offences had taken place during only three of his 24 years in teaching.

''However repulsive these activities were, the accused managed to stop this conduct and appears to have come to his senses at the end of the seventies,'' he said.

Forsyth, divorced with a grown-up family who live abroad, retired when the offences were discovered. Mr McLeod had asked his client why he had done it. ''All he could offer by way of an answer was that his marriage was in a profoundly unhappy condition at that time.''

After the offences came to light Forsyth had tried to rebuild his life and had received counselling, which appeared to be successful. There were gasps of disbelief from victims and families when Mr McLeod said: ''So successful, he has recently obtained a national certificate in counselling.''

He said that before a previous scheduled court appearance on the charges Forsyth had attempted to take his own life.