The school devised a plan to minimize contact between Ms. Bostick’s daughter and the accused, but her requests that they have zero contact and that he ultimately be removed from the school were rebuffed. After losing two Title IX appeals, the girl transferred to a private school nearly an hour away. The Virginia state legislature recently passed a bill named after her that would protect students with protective orders in school.

“Every choice those adults made was devastating to her,” said Ms. Bostick, who teaches Latin at the school. “There was nothing we could do, nothing we could show that would make them have compassion for her. The proposed changes would make our nightmare the new standard.”

Jason Van Heukelum, the superintendent for the school district, said its conclusion was based on two exhaustive weekslong investigations that included reviewing nearly 1,300 pages of documents and conducting 17 interviews.

“We go to great lengths to afford our students and staff protections from the violation and the fear of assault and harassment in our schools,” he said.

Though colleges get the attention, it was a K-12 case that spurred the Supreme Court to expand the law to include student-on-student assaults. In 2016, the Obama administration issued guidance to K-12 schools as part of its overhaul of campus rules on sexual assault. The administration had seen a jump in sexual violence complaints in K-12 systems, to 83 in 2016 from 11 in 2009.

Even then, advocates and civil rights officials believed those numbers were grossly underreported, because school districts failed to recognize when children were articulating sexual harassment.

“If you don’t recognize sexual violence, you’re going to perpetuate it,” Ms. Kimmel said.

The Obama administration’s investigations into K-12 systems revealed some of the most egregious violations, Ms. Lhamon said. She said the civil rights office often encountered a “school’s insistence that they didn’t need to have standards because students shouldn’t be having sex.”