She had to have her lessons separately from the rest of her class. And now she's been sent home and told not to come back til the gem's been removed.
But Rachel, and her mum, Elaine, are livid.
Rachel's dentist has said they'll have to clamp her tooth and scrape it off, which could shatter the Ģ15 gemstone and scratch the enamel on her tooth.
Drop off naturally
Rachel's mum, who paid for the gem, said: "I'm not prepared to have it taken off that way when it's going to drop off naturally between six and eight months away.
"If I thought it would have caused a problem I would never have had it done."
But the school said there's no difference between a tooth gem and a nose stud, and that the pupils have been warned in the past that they're banned.
And dental experts said tooth gems could normally be removed without harming the teeth.
What do you think about this story? Are schools too strict about uniforms and jewellry? Or did the girl get what she deserved?
In the Netherlands we think it's very stupid of the school. At our school everyone weares that kind of things!
Kim, 16, Netherlands
"I think she was fine - it's only a small jewell really."
Jemma, 12, Canterbury
"I can't understand what her mum was thinking of. What a bad example of parenting."
Graham, 14, Canterbury
"schools r so strict wit fashoin! Just cos the teachers have no sense of fashion at all, dosnt meen we cant!"
Kim, 13, Blackpool
"Why make such a big deal? They shouldn't have banned her from school. That's really out of order."
Chloe, 11, Brighton
"I think that her parents should spend the money on braces, not a tooth gem!"
Amy, 14, New York
"How is a tooth gem dangreous? It's not even that noticable! A student's body is their own. If they want to get a nose stud, let them. Its no different then having a pierced ear."
Rachel, 14, New York
"Is it dangerous? I donīt think so."
Kim, 13, Sweden