Kate Norfolk (centre) expected a grade A at Latin
Kate Norfolk, who attended £4,000 per term independent school Hurstpierpoint College, West Sussex, says she was not properly prepared for her Latin A-level.
The former pupil, who got an A in history and a B in French, claims the poor result in her third A-level will affect her chances of working as a top corporate lawyer.
Her family has issued a writ to the High Court, seeking £150,000 to cover the loss of future earnings, school fees and compensation for the distress caused.
Hurstpierpoint College described the matter as a "one-off event" and said the claim was out of proportion to the circumstances.
Kate, who sat her A-levels last summer, is now studying for a degree in ancient and modern history at Exeter University.
'Bright girl'
Her father, Robert, said Kate was a very bright girl who had worked very hard and had been predicted a grade A in Latin.
"They didn't study the syllabus - it was a new teacher and he didn't seem to know what he was doing," said Mr Norfolk.
"But they weren't individually contacted or given any explanation - it was chance one of them saw it.
"The school plainly didn't do what the prospectus or the head teacher said they would do prior to us putting her into the school at age 13," he said.
Kate feared she would now fail to be shortlisted for interview at the very top law firms, he said.
"She wants to be a corporate lawyer and she wants to be a good one - she's always been a bright and ambitious girl," said Mr Norfolk.
School regrets
In a statement, the head teacher, Stephen Meek, said the college greatly regretted the circumstances that led to an action being taken.
"The weakness in Kate's Latin teaching was a lapse by a young teacher who came to us with a good reference and experience of teaching Latin," said Mr Meek.
"The teacher in question is no longer with us having taken up an appointment in industry.
"We have of course taken steps to ensure that such a lapse cannot occur again," he said.
The school had an excellent academic and pastoral record, he added.
"There are elements in the writ that we will strongly contest and we believe the claim to be out of proportion to the circumstances," he said.