A fraud investigation is underway after pupils reported already seeing the papers for their 11-plus English and Maths exams, Plymouth City Council has confirmed.
The security breach will mean hundreds of girls are forced to re-take their exams next month.
The girls - who were competing to gain a place at Devonport High School for Girls and Plymouth High School for Girls - had allegedly been given the papers as part of a practice exam.
A spokesperson for Plymouth City Council said: ‘We regret to announce that due to a security breach, the candidates who sat the papers are going to have to re-sit them, and while we recognise that this is not ideal, it is the only way we can ensure the tests and admission process are carried out fairly. Investigation into the source of the breach is ongoing.
‘This is now being treated as a fraud investigation and a police matter so we are working closely with GL Assessment and fraud investigators, but we cannot comment further at this stage until the investigation is complete.’