Amanda, 15, was sent home from Bournside School more than two weeks ago after having her upper lip pierced.
Her mum Joanne, from Surrey Avenue, Warden Hill, says the school’s actions mean Amanda’s education has suffered.
But the school, in Warden Hill Road, says parents are aware of the dress code and it’s Joanne’s choice not to send Amanda to school appropriately presented.
Joanne says she has tried to compromise with the school by offering to put a plaster over the piercing and replacing the metal stud with a clear one.
She said: “They sent her home. She tried to go back with a clear stud but they wouldn’t let her.
“It’s only a stud. I can’t see anything wrong with it. It’s not as if it effects her sitting in a classroom learning.
“I’ve tried to compromise but the school keeps saying it’s unacceptable and it won’t be tolerated. The clear stud is nowhere near as noticeable. I can’t see what all the fuss is about.
“Amanda is now in her third week of no school and I’m concerned.”
Bournside headteacher Alan Foulds said: “We’re clear and consistent about uniform expectations at Bournside. We publish them openly to every parent, who accepts and agrees to abide by them.
“The choice not to come to school is that of the parents because they know what’s expected of them and their child.
“Ignoring that is of concern and naturally she will be falling behind.
“Parents must understand our expectations and we have outlined this to them.
“We hope to see her return to Bournside shortly. This is an unusual and isolated incident.”
Gloucestershire County Council cabinet member for schools Coun Joan Nash, said: “It’s up to schools to impose rules on uniform but it’s important that children and young people are in school.”