Coy Mathis's family raised the issue after school officials said the first-grader could use restrooms in either the teachers' lounge or in the nurse's office, but not the girl's bathroom at Eagleside Elementary School in Fountain.
Kathryn and Jeremy Mathis have said the district's decision would end up stigmatizing their daughter, who they said had come out of her shell when they began to allow her to live as a girl, instead of a boy.
The Colorado Division of Civil Rights found probable cause of discrimination in a letter dated June 18. The New York-based Transgender Legal Defense and Education Fund announced the ruling in favor of Coy on Sunday.
Lawyers plan to explain the ruling Monday in Denver.
Since they filed their complaint, the Mathises have moved to the Denver suburb of Aurora, and Coy was homeschooled. It wasn't immediately clear whether the family would enroll her in the new district.
Fountain-Fort Carson School District 8 has declined to discuss the case. The district, however, can seek arbitration or a public trial, said Cory Everett-Lozano, a spokeswoman with the Colorado Department of Regulatory Agencies.
The Mathis' attorney, Michael Silverman, said it wouldn't make any sense for the school district to fight the ruling since Coy and her family are no longer in the district. "Our hope is that the case ends here," Silverman said.
School districts in many states, including Colorado, allow transgender students to use the bathroom of the gender with which they identify. Sixteen states, including Colorado, have anti-discrimination laws that include transgender people.
In Maine, the state's highest court heard arguments this month about whether school officials violated the rights of Nicole Maines, now 15, by requiring her to use a staff bathroom after there was a complaint about her using the girls' bathroom.
The Mathises said Coy, a triplet, showed an early preference for things associated with girls.
At 5 months, she took a pink blanket meant for her sister Lily. Later, she showed little interest in toy cars and boy clothes with pictures of sports, monsters and dinosaurs on them. She refused to leave the house if she had to wear boy clothes.
They said she became depressed and withdrawn, telling her parents that she wanted to get "fixed" by a doctor.
They said they later learned she had gender identity disorder -- a condition in which someone identifies as the opposite gender. The Mathises said they decided to help Coy live as a girl and she came out of her shell.
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