Dr Ian Garrero rejected suggestions that his action in buying 16-year- old Sabrina Cohen an pounds 8.99 Beatles-style wig had been ridiculous. He said yesterday that his aim had been to protect other pupils.
"She arrived with a dog, without a uniform, with a pierced lip and her dyed hair. This would have created an unreasonable environment for other students to do their best," said Dr Garrero, head of Bassaleg Comprehensive School in Newport, south Wales.
School rules prohibited "bizarre hairstyles", and the only piercing allowed was of ear lobes. "Strange hairstyles could distract other pupils from getting on with their exams," said Dr Garrero.
Miss Cohen, who is forecast to achieve top grades in the 11 GCSEs she is sitting, was originally ordered to dye her hair back to its original brown.
In a compromise, the school said it would pay up to pounds 10 for a wig for her to wear in the exam hall and for plasters to mask her facial piercing.
Dr Garrero added: "The school has given Sabrina every opportunity to take her exams and it was for health and safety reasons that we asked her to cover her lip."
Miss Cohen said: "I can't see why red hair makes any difference to my ability to sit and pass exams."
She had wanted to buy an Afro wig, "but my tenner didn't stretch that far. In the end I had to settle for the Beatles, which is not really my scene".