Pupils have been banned from wearing tinsel to a non-uniform day because teachers say it could cause litter and be dangerous.
Staff at Chipping Sodbury school say the tinsel could cause injury if pupils tried to strangle each other.
Children were sent home with a letter citing "health and safety reasons" for the ban.
South Glos Council said the day was "far from being against the spirit of Christmas" and was in aid of Crisis.
The school refused to comment but a 16-year-old pupil sitting mock GCSEs at the school said: "It is awful to ban tinsel. It is supposed to be a festive celebration at the end of term, a bit of fun, and I think to ban tinsel is PC
"It is just silly, we all know not to go around strangling each other," the student added.
The teenager said the ruling was pointless as pupils could still wear boas, Santa hats and novelty earrings on the last day of term.
On behalf of the school, a council spokesman said: "The decision to stop pupils wearing tinsel on non-uniform day was taken mainly as a result of the school's campaign to clamp down on litter.
"We, as a school, constantly strive to provide a safe working environment for our students and health and safety is of utmost importance."