(CNN) -- A transgender first-grader who was born a boy but identifies as a girl has won the right to use the boys' restroom at her Colorado school.
The Colorado Rights Division ruled in favor of Coy Mathis in her fight against the Fountain-Fort Carson School District.
Coy's parents had taken her case to the commission after the district said she could no longer use the girls' bathroom at Eagleside Elementary.
In issuing its decision, the state's rights division said keeping the ban in place "creates an environment that is objectively and subjectively hostile, intimidating or offensive."
Coy's mother, Kathryn Mathis, said she's thrilled that Coy can return to school and put this behind her.
The first-grader has been home-schooled during the proceedings
"Schools should not discriminate against their students," Mathis said. "All we ever wanted was for Coy's school to treat her the same as other little girls. We are extremely happy that she now will be treated equally."
Mathis and her husband Jeremy will hold a noon (2 p.m. ET) news conference to discuss the case.
The Transgender Legal Defense & Education Fund praised the ruling that was filled under Colorado's Anti-Discrimination Act.
"It is a victory for Coy and a triumph for fairness," said Michael Silverman, the group's executive director. "This ruling sends a loud and clear message that transgender students may not be targeted for discrimination and that they must be treated equally in school."
A girl's life
For most of the past year, Coy has dressed as a girl.
Coy's passport and state-issued identification recognize her as female.
Mathis said she got a call "out of the blue" from the school in December saying that Coy could use the boys' bathroom, gender-neutral faculty bathrooms or the nurse's bathroom, but not the girls' facilities.
The district "took into account not only Coy, but other students in the building, their parents and the future impact a boy with male genitals using a girls' bathroom would have as Coy grew older," a letter the family's attorney received in December said.
"However, I'm certain you can appreciate that, as Coy grows older and his male genitals develop along with the rest of his body, at least some parents and students are likely to become uncomfortable with his continued use of the girls' restroom."
CNN was unable to reach the school district early Monday for comment on the ruling. But in February, the district's attorney, W. Kelly Dude, said: "The district firmly believes it has acted reasonably and fairly with respect to this issue."
A little-studied group
Transgender children experience a disconnect between their sex, which is based on their anatomy, and their gender, which includes behaviors, roles and activities, experts say.
For the general public, transgender identity may be a new concept, though many might recall Chaz Bono, the child of entertainers Sonny and Cher. Born female, Bono underwent a transition in his 40s to become a man. He wrote in his book "Transition" that, even as a child, he had been "aware of a part of me that did not fit."
He appeared last year as a man on "Dancing with the Stars," in part, he said, to destigmatize being transgender.
Comprehensive data and studies about transgender children are rare. International studies have estimated that anywhere from 1 in 30,000 to 1 in 1,000 people are transgender.
Some children as young as age 3 show early signs of gender dysphoria or gender identity disorder, mental health experts who work with transgender children say.
These children are not intersex -- they do not have a physical disorder or malformation of their sexual organs. The gender issue exists in the brain, though experts do not agree on whether it's psychologically or physiologically based.
Many transgender people report feeling discomfort with their gender as early as they can remember.
Gender identity is often confused with sexual orientation. The difference is that "gender identity is who you are, and sexual orientation is who you want to have sex with," said Dr. Johanna Olson, a professor of clinical pediatrics at the University of Southern California, who treats transgender children.
Children around age 3 are probably not interested in sexual orientation, she said. But experts say some children who look like they will be transgender in early childhood turn out to be gay, lesbian or bisexual.
Differences in schools
School policies toward transgender students vary across the United States.
In New York, for example, the law says students can't be discriminated against on the basis of their gender identity.
But in Maine, a court ruled in November that a school district did not violate a transgender student's rights when she was told she couldn't use the girls' bathroom.
Dude, the Colorado school district's attorney, has said there is nothing in that state requiring public schools to permit transgender students to use restrooms intended for the gender with
which they identify.
At the time, he argued that the Fountain-Fort Carson School District adheres to the Colorado Anti-Discrimination Act in all respects: "Coy attends class as all other students, is permitted to wear girls' clothes and is referred to as the parents have requested."
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