A school that barred a Muslim girl who wanted to wear traditional "head-to-toe" dress behaved illegally, an appeal court has been told.
Shabina Begum wants to wear a full-length jilbab gown
Shabina Begum, 15, has not been attending Denbigh High School in Luton since September 2002 in a row over her wish to wear a jilbab.
Cherie Booth, QC, told the court on Monday the case involved Miss Begum's right to practise her religion.
The case has important implications for multi-faith schools across the country.
Miss Booth said the case involved "fundamental issues" about the nature and interpretation of Miss Begum's rights to education.
"Her rights to manifest her religious beliefs should be respected," she said.
Six months ago, High Court judge Mr Justice Bennett dismissed the girl's application for judicial review, ruling that she had failed to show that the "highly successful" 1,000-pupil Denbigh High School, with 79% of its students Muslims, had excluded her or breached her human rights.
Miss Booth said the judgment of Mr Justice Bennett was saying the school, which sent Miss Begum home after she refused to wear authorised school uniform, is entitled to "pick and choose" which religious beliefs it accepts.
She said: "The school is saying it is not willing to accept your particular religious beliefs."
Lord Justice Brooks, the vice-president of the Court of Appeal Civil Division, said the case involved one particular race and culture in a multi-cultural society.
He asked whether any child who holds a particular belief sincerely should be able to ignore school uniform codes.
He asked: "How do you cope with that?"
Miss Booth said this was not a Race Relations Act case, but that either countries (such as Switzerland and France) can impose secular dress for everyone in school, or they can respect diversity and allow schoolchildren to express their religious beliefs.
"I say our policy is to respect diversity, and it is not for the public authority to judge which beliefs are more valid than others," she said.
To win the appeal, it will have to be proved that Miss Begum is being excluded from school and being denied her "right to education and to manifest her religious beliefs".