Mrs Playfoot said: "The ring is a reminder to them of the promise they have made, much the same as a wedding ring is an outward sign of an inward promise.
"There are Muslim girls at the school who are allowed to wear the headcovering, although that isn't part of the school uniform, and Sikh girls who are allowed to wear the bangle, although that isn't part of the uniform.
"It's a discriminatory policy. We don't want her education to be disrupted because of it but we do want her to feel free to wear something that is very significant."
Headmaster of Millais, Leon Nettley, said in a statement that the sex education programme currently run in the school already warned pupils of the illegality of under-age sex and encouraged pupils to discuss the issues.He added: "In relation to the issue of wearing a purity ring, the school is not convinced that pupils' rights have been interfered with by the application of the school's uniform policy.
"The school has a clearly published uniform policy and sets high standards in this respect."
Silver Ring Thing was started up in the US eleven years ago by father-of-three Denny Pattyn in Yuma, Arizona, after he found out that they city had the highest teenage pregnancy rate in Arizona.
Each ring is imprinted with the Bible verse 1 Thessolonians 4:3 – 4 which says: "For this is the will of God, even your sanctification, that ye should abstain from fornifi-cation: That every one of you should know how to possess his vessel in sanctification and honour."
The movement has proved highly successful in encouraging a number of teenage girls to make a commitment to keeping their chastity until marriage and the silver bands are worn as a sign of commitment to that pledge.
Silver Ring Thing hit the UK in 2004 to promote to British teenagers abstinence before marriage.
Mr Pattyn said when he brought the campaign here, “Silver Ring Thing evening are cool and fun and full of life,” adding that the ring “is important”.
“It’s a visible sign of the pledge and a constant reminder”.
The issue of wearing purity rings was raised in the Commons last week by Tory MP Andrew Selous, chair of the Conservative Christian Fellowship, before the Schools Minister Jim Knight.
Mr Knight said in a written parliamentary answer that while school governors had the right to set the uniform rules, government guidance also states that they “should have regard to their responsibilities under equalities legislation” and be “sensitive to pupils’ cultural and religious needs”.
