To him, the right one is the boys' bathroom, which he says he has used since seventh grade without incident. Then, in his senior year, school administrators told him he had to use the girls' restroom, he said. They also gave him the option to use the nurse's restroom.
When he exited the bathroom, the teacher did not say anything to him, but he knew from the "exasperated" look on her face that he was in trouble.
The next morning, he was called into the vice principal's office and told he was suspended for one day for using the boys' bathroom.
"I started having a panic attack," he told CNN. "Teachers should never be following students to the bathroom unless they reek of cigarette smoke or alcohol."
He asked to be identified as R. because, like many transgender people, he does not want to publicly identify as transgender. He simply wants to spend his days in the skin he feels comfortable in.
Instead of returning to school less than three months before graduation, he enrolled in online classes for fear of being "outed." Now, he's threatening legal action against Horry County Schools to make sure other transgender students don't have to experience what he went through.
A case to test transgender rights
CNN could not independently confirm the student's claims, which were laid out in a demand letter from the Oakland, California-based Transgender Law Center sent Thursday on R.'s behalf. It appears to be the first test of last week's appeals court decision
that upheld transgender students' rights to use bathrooms consistent with their gender identity.
In that case, the 4th Circuit Court of Appeals ruled on April 19 in favor of Gavin Grimm, a Virginia teen who claimed that the Gloucester County School Board violated Title IX
, a federal law banning sex discrimination in schools, by preventing him from using boys' restrooms in school.
The decision is binding on nine federal district courts in Maryland, Virginia, West Virginia, North Carolina and South Carolina, meaning judges are compelled to follow it as precedent.
It remains to be seen how lower courts in the conservative circuit will interpret the decision. In addition to school policy, it could impact legislation such as North Carolina's controversial law
prohibiting transgender people from using public restrooms for the gender they identify with.
The decision created an opportunity to show that similar school district policies within the circuit are just as unconstitutional as Gloucester's policy, said Ilona Turner, legal director of the Transgender Law Center.
Horry County Schools Superintendent Rick Maxey would not comment specifically on the allegations but said the district is working to create a "welcoming environment."
"The district maintains the privacy of all of its students," Maxey said in an email. "The district seeks to accommodate the individual needs of its transgender students in compliance with the law, including Title IX. We will continue our efforts to ensure a welcoming school environment for all students."
After R. was suspended in January, a representative for the schools told CNN affiliate WMBF
that the district does not have a specific policy on bathroom use for transgender students. The representative said the district makes accommodations based on individual needs and schools.
The Transgender Law Center's letter asks the school district to remove the suspension from R.'s record. It also asks the district to give transgender students access to facilities that match their gender identity and to ensure that all school staff respect the gender identity of transgender students. If the school does not comply within a week, center officials might file a complaint with the Department of Education, which enforces Title IX. Another option is to file a lawsuit in federal court, similar to the Grimm case.
"It's a very dangerous thing when we create these kinds of policies and laws intended to single out transgender people. They have the effect of policing everyone and placing gender under scrutiny," Turner said.
"Anyone who walks into a women's restroom who has short hair or appears less than totally feminine may have the police called on them or asked for their birth certificate."
'It was hard to understand'
For years, it appeared that the school was on board with R.'s gender identity, said the teen and his mother, who asked to go by Lynne.
Though he was born a girl, he resisted wearing dresses and began to show signs of identifying as a boy when he was 4, Lynne said.
It was difficult for her to accept initially, especially in a conservative community where traditional gender roles reign, but in the end she just wanted her son to be happy, she said.
"It was hard to understand what transgender was because I had never heard of it before," she said. "I had to get to place where I understood what that was and what it means."
By seventh grade, R. was shopping for clothes from the boys' section. Based on his appearance, girls in middle school began to complain when he used the girls' room. His family reached a decision with school administrators to use the boys' room to make everyone more comfortable, his mother said.
Since then, he has used the boys' room at school and in public places, Lynne said. Except for family and a few close friends, people at school knew him as a boy, until October. That's when a teacher found out he was born a girl and complained to administrators about him using the boys' room, the law center's letter states.
His mother met with school administrators and told them they had to let her son use the bathroom according to his gender identity. They disagreed and said that he must use the girls' room or that he could use the nurse's room, the letter says.
Using the girls' room was not an option, he said. He did not want to be outed after years of living as a boy. He chose the nurse's room to make it less obvious, but it soon proved onerous: The nurse's bathroom is on the first floor and most of his classes were on the second or third floors, he said.
Each time he went to the bathroom, he lost about 10 minutes in classroom time. Occasionally, to save time, he disobeyed the mandate and used the boys' room to save time.
"It was a lot of walking. I was always worried about how long I was out of the classroom," he said.
The worries turned into panic attacks at school, which were exacerbated by teachers who started using female pronouns to refer to him, according to the demand letter.
The January confrontation outside the bathroom was the tipping point, Lynne said. Instead of returning to school after the suspension, he enrolled in online courses. It was no longer just about the panic attacks or the inconvenience of using the nurse's bathroom, his mother said.
After years of treating him like a boy, the school was effectively outing him, she said.
"I was mad. I was angry, very angry that they would treat my child that way after all these years," she said. "I don't understand why it's important to dictate which bathroom they're allowed to use. I don't understand why people feel the need to control other people's lives."
Incidentally, R.'s progress in school has improved since he started classes online through the state, he said. His grades are better, and he's on track to finish classes ahead of time.
Regardless of whether the school grants his request, he feels a duty to future students to fix the situation.
"That's kind of my job, as a senior at the school," he said. "People should be able to use the bathroom in peace without being policed for using the right one or the wrong one."