An international school yesterday denied firing a teacher because she refused to give the then principal's son an 'A' in his maths exam, a Labour Tribunal heard. Ruth Prevenslik, who taught at the American International School until her dismissal on February 12 last year, said the wife of former principal Dr Thomas Hart insisted she change their son's grade from a B-plus to an A. When she refused, Mrs Hart threatened indirectly that Ms Prevenslik would lose her job, the teacher claimed. 'I was asked to do something unethical. And had I done what she asked, it would have been fraud on my part.' But while this contributed to her dismissal, she claimed this was only a smokescreen and that the main reason was her union activities. 'I was fired just three hours after I sent out a union newsletter [from the Professional Teachers' Union] and application forms to about 20 to 30 teachers,' said Ms Prevenslik. Current principal Elsie Gee said Ms Prevenslik was fired because she breached professional integrity by circulating to teachers a letter about the alleged exam incident on February 1, 1999. 'This is a breach of confidentiality as teachers are asked not to discuss children specifically.' Ms Prevenslik also failed to justify her decision to exclude the results of a test in the final grades of students, she said. Mrs Gee denied the dismissal was due to Ms Prevenslik's union activities. Ms Prevenslik is claiming more than $211,500 in damages for unreasonable and unfair dismissal.The proceedings continue today.