Transgender and gender-nonbinary youth are more likely to have experienced sexual assault or harassment if they attend a school that does not permit them to use bathrooms and locker rooms that correspond to their general identity, according to a study released Monday in the journal Pediatrics.

“We can’t tell from this study whether restrictive restroom and locker room policies cause sexual assault,” said lead study author Gabriel Murchison of the Harvard T. H. Chan School of Public Health in Boston. “However, at the least, they seem to be a marker for an environment where trans and nonbinary youth are at risk.”

Of the 3,673 trans and nonbinary middle school and high school students surveyed across the United States, 26 percent reported being sexually assaulted in the previous 12 months. Among those who attend schools that restrict their bathroom and locker room access, the percentage jumps to 35 percent.

And transgender girls — who identify as female but were assigned male at birth — had more than twice the assault risk when they had to use restrooms and locker rooms for boys.

The report’s authors also found trans and nonbinary students experienced sexual assault at “troubling rates well above those for nontransgender adolescents.”

“All families want their children to feel safe at school, and many know that restrooms and locker rooms can be problem areas for bullying and harassment,” Murchison said in an email to NBC News. “With better information about the problem, families and schools can work together to address it.”

Addressing the issue, he added, “can include better supervision of locker rooms, more privacy options (like curtained changing areas), and an effective and consistent school response to harassment.” The study also suggested that schools seriously consider “all-gender restrooms.”

Even though there are few “bathroom bills” on the books across the U.S. — LGBTQ advocates have fought them in court for years — most transgender students report that they are not free to use the boys or girls facilities that correspond to their gender identity. In many jurisdictions, schools force students to use facilities that correspond to their biological sex, or force them to use unisex facilities, which the study says may put them at additional risks.

“Although we cannot determine if the restrictions themselves affected safety, it appears that using a single-person facility (eg, a staff restroom) may not fully address the risks associated with restrictions,” the report stated, because doing so may “out” a student as transgender.

The authors relied on data from the LGBTQ Teen Survey, an online study conducted by the Human Rights Campaign and researchers at the University of Connecticut. Out of more than 17,000 respondents, the researchers identified 3,673 youth who were in grades 7 through 12 and identified as transgender and/or gender nonbinary.

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