The move is another sign that school systems in the Washington region are embracing transgender students, despite forceful opposition from some community members and broader national clashes over rights for lesbian, gay, bisexual and transgender people. In recent years, school boards in northern Virginia have expanded protections for transgender students and updated curriculums to be more inclusive.
Referring to experiences in their own schools, the four systems wrote that allowing transgender students to use the restrooms aligning with their gender identity makes the students feel safer and more accepted, and they rejected fears commonly cited by those who oppose doing so.
"Male students, teachers, and parents have not used the policy as a ruse to improperly access female restrooms. Sex offenders have not exploited the policy to prey on children. Transgender students have not suffered greater stigma or trauma," the brief states. "Those fears have proved entirely unfounded."
All of the northern Virginia school systems that signed onto the brief have approved measures prohibiting discrimination based on gender identity. The policies don't expressly guarantee students access to restrooms that match their gender identity, but schools work to accommodate students' requests individually.
Activists who support transgender rights say students should have access to facilities that match their gender identity.
The Fairfax County School Board considered regulations in 2016 that would have spelled out how schools should accommodate transgender students, including a rule that would have affirmed students' right to use bathrooms that correspond with their gender identity.
But Fairfax, the largest school system in Virginia, chose not to move forward with the proposals because it wanted to evaluate court cases and other legal issues, including Grimm's.
The outcome of Grimm's case appears likely to influence the Fairfax board's decision on its own regulation, said Ilryong Moon, the Fairfax school board member who advanced the idea of issuing an amicus brief.
"It's a perfect opportunity for us to show support for Grimm," Moon said, adding that Fairfax schools want to "support all students of different backgrounds."
In the Falls Church school system, which has about 2,620 students, schools work with students and parents "to come to an agreement on the best way to support the student," which has included the use of gender-neutral bathrooms in the city's middle and high schools, spokesman John Wesley Brett said.
Six gender-neutral changing rooms, each equipped with a toilet, shower and dressing area, will be included in the city's rebuilt high school when it opens in 2021, Brett said. Gender-neutral bathrooms are planned throughout the school.
Arlington's school system is developing procedures to uphold its nondiscrimination policy, including a regulation that would permit students to use restrooms that correspond to their gender identity, spokeswoman Catherine Ashby said. The procedures are slated to be finalised in June.
The northern Virginia school systems' approaches stand in contrast to a policy adopted by the Gloucester County School Board that required students in the Chesapeake Bay community to use restrooms that align with their "biological genders."
The mandate meant that Grimm was barred from the boys' restroom at Gloucester High School during his sophomore year, prompting a 2015 lawsuit against the school system.
The case reached the Supreme Court, where it was scheduled to be heard until Education Secretary Betsy DeVos and then-Attorney General Jeff Sessions rescinded the Obama-era position that students should use bathrooms that align with their gender identity.
Federal anti-discrimination law, they argued, did not require schools to let transgender students use the bathroom of their choice. The reversal sent Grimm's case back to a lower federal court.
Grimm, now 19, is studying to become a middle school teacher in California.
The issue of whether to provide protections for transgender students has divided communities across the country. Those who oppose letting transgender students use the bathrooms they prefer argue that doing so could jeopardize other students' safety and privacy.