A leading transgender rights group on Thursday announced that the Colorado school which has barred 6-year-old transgender girl Coy Mathis from using the girls' bathroom at her elementary school has refused mediation to settle the dispute.

The Transgender Legal Defense & Education Fund (TLDEF) filed a complaint with the Colorado Civil Rights Division after Coy's parents, Jeremy and Kathryn Mathis, were told in mid-December by the Fountain-Fort Carson School District 8 that Coy could no longer use the girls' bathrooms that she had been using for the past year at Eagleside Elementary School in Fountain, where she is a first-grader. Coy was told she could use the nurse's bathroom, a staff bathroom used by adults, or the boys' bathroom.

“Coy is not sick, she is not an adult, and she is not a boy,” the Mathises said in a statement. “If the school separates her from all her classmates to use the bathroom, they are singling her out for mistreatment, and teaching her classmates that it's okay to discriminate. We are saddened that her school will not even come to the table to talk about this issue.”

More than 23,000 people have joined an online petition calling on the school to reverse its decision.

“We are so thankful for this show of support for our daughter,” the Mathises said.

“These signatures should show Coy's school that they are on the wrong side of this issue,” said GLAAD President Herndon Graddick. “All kids need to feel welcomed by their communities. Thankfully, thousands of Americans are sending Coy the right message, even as her school is still insisting on sending the wrong one.”