By Ed Payne and Ashley Fantz
(CNN) -- A prominent transgender rights group announced Wednesday that it has filed a discrimination complaint in Colorado on behalf of a first-grader who was born a boy but identifies as a girl.
Last December, school officials at Fountain-Fort Carson School District told Coy Mathis' parents that their child could no longer use the girls' bathroom at Eagleside Elementary.
That shocked her parents, said her mother, Kathryn Mathis.
Coy was born with male sex organs but has, since she could express herself, identified as female. The child had gotten through kindergarten with no problems and no complaints from anyone at the school, Mathis said.
The mother was flanked at a press conference at the Colorado Capitol in Denver by her husband, Jeremy, and four other children.
Wearing a feminine winter coat, Coy stood behind her mother.
Kathryn Mathis explained that she pulled Coy out of school when the child was on winter break, well after school officials had called her to tell her about the bathroom ban.
The mother feared that bullies at the school would make fun of her daughter if she allowed Coy to go back to class.
"In the end we just want what is the best for Coy," Mathis said, explaining why the complaint was filed. "We want her to be able to go back to school and be treated equally without discrimination and harassment."
Attorney Michael Silverman of the Transgender Legal Defense and Education Fund, which is representing Coy, said the complaint is intended to have an impact beyond a single family or school.
The complaint was filed with the Colorado Civil Rights Division.
"For many transgender people, discrimination is a daily part of life. Unfortunately for Coy, it has started very early," he said, adding that the complaint is a "test of Colorado's Anti-Discrimination Act."
"The world is going to be looking at the school," he said, which can "send a message to the world and teach tolerance, fair play and equal rights."
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.
Kathryn 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," the school district's attorney, W. Kelly Dude, told CNN Tuesday.
"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."
An unstudied group
Transgender children experience a disconnect between their sex, which is anatomy, and their gender, which includes behaviors, roles and activities, experts say.
For the general public, transgender identity is a somewhat new concept, though many might recall Chaz Bono, who was born female to entertainers Sonny and Cher and appeared on last year's "Dancing with the Stars," in part, he said, to destigmatize being transgender.
In his 40s, Bono underwent a transition to become a man. He wrote in his book "Transition" that even in his childhood, he had been "aware of a part of me that did not fit."
Comprehensive data and studies about transgender children are rare. Various international studies have come up with different numbers for the rate of transgender people in the population, ranging from 1 in 30,000 to 1 in 1,000.
Some children as young as 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 whether it's psychological or physiological is debated by experts.
Many transgender children report feeling discomfort with their gender as early as they can remember.
Gender identity often gets 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.
In Maine, on the other hand, 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 girl's restroom.
Dude, the Colorado school district's attorney, has said there is nothing in that state requiring public schools to permit transgender students to use the restrooms of the gender with which they identify.
He added 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."
She also has easy access to bathrooms other than the girls' restroom, Dude said.
Coy's case will be the first to challenge relating to a restroom restriction under the state's anti-discrimination act, the Transgender Legal Defense and Education Fund said.
For now, the first-grader is being home-schooled.
Reaction to Coy's story
CNN's online audience responded to this story with a range of questions and comments, with many saying the child is far too young to comprehend gender differences. Mostly, posters said they felt a great deal of sorrow for Coy as a child who is struggling.
"Just let the kid use the gender neutral bathrooms. When he/she is a teen, if he is still convinced he is a girl, maybe then you can get into it with the school," said commenter EDM.
"This kid is going to have a hard enough life if he really is transsexual, why start fighting battles now, when he should just be blissfully ignorant"?
Commenter AlawJ said the story left a "negative impression of the parents."
"My rash view may be unfair, but I remember being that age and have helped raise 9 nieces and nephews. One wanted to be a firetruck and ran around making truck noises. Another one of the boys liked to play dress up with the girls," AlawJ wrote. "My fiance's little brother always wore dresses as well. But, at the end of the day, the parents are there to be the adults and make decisions for them.
"I also am a little weary when you read a story where the parents are filing lawsuits for their 6 year old child's rights."
Other commenters had harsher words for Coy's parents. "How about this boy's parents stop abusing him and putting ideas into his head. Don't dye his hair and send him to school in jeans and a t-shirt. Have them stop using their son for their own 15 minutes of fame," wrote Metamatic.
MRHD81 wrote, "There is NO WAY a first grader came to a decision like this -- this is parents abusing/brainwashing their kid to make a statement."
Coy's awareness of being a girl or boy comes, the poster believes, "from life experiences, physical development and other factors that a first grader would not have been yet exposed to."
Commenters also wondered what Coy's former classmates think, asking what would happen if Coy later wanted to play sports and use the girls' locker room.
CNN's Cristy Lenz and Madison Park contributed to this report.