In December, however, when Coy, 6, was a few months into the first grade, the Mathises angrily pulled her out of school after being told that she could no longer use the girls’ bathroom but could instead use a gender-neutral restroom.

A letter from a lawyer for the Fountain-Fort Carson school district explained 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.”

Now, Coy’s case is at the heart of legal dispute that is likely to test Colorado’s anti-discrimination law, which expanded protections for transgender people in 2008.

The case is unfolding in this small town just south of Colorado Springs, as other states across the country seek to clarify their policies relating to transgender students.

It is an issue that has become more commonplace in recent years as advocacy groups push to ensure that school districts are more attuned to the needs of transgender children.