A 15-year-old girl and her mother are suing a private school in the Northern Virginia suburbs and its administrators over their handling of an alleged sexual attack by a classmate.

The girl, identified in court papers as Jane Doe, was a student at Congressional School in Falls Church when she said a male classmate assaulted her on a bus as they arrived home from a school trip to New York on April 1, 2017, the lawsuit states.

Shortly before the bus pulled into a Rosslyn location where parents were to meet their children, the 14-year-old boy, who was not identified by name in court papers, “violently pulled” the girl on top of him and reached under her dress to forcibly touch her genitals, the lawsuit alleges.

A. Joseph Jay III, an attorney representing Congressional, rejected the allegations. The school hired the Sheppard Mullin law firm to investigate after it received a draft of the lawsuit in summer 2018, he said.

“Given the gravity of these claims, Congressional School promptly retained counsel to thoroughly review these matters,” Jay said in a statement. “We have done just that. The facts do not support the allegations raised in the complaint and thus, these claims are without merit.”

The lawsuit was filed in Fairfax County Circuit Court on March 22.

The mother said in an interview that the alleged encounter altered her daughter, who was 13 at the time.

“Before this happened, she was a fairly happy, outgoing person,” the mother said. “Then everything changed and she became withdrawn, angry, depressed. . . . She told me she couldn’t trust anyone.”

The Washington Post generally does not identify alleged victims of sexual assault without their express permission.

The family says the girl’s physical and mental health issues were “caused or exacerbated” by the school, according to the lawsuit. They are suing for at least $2.35 million in damages, the suit states.

Congressional School is on a 40-acre campus that boasts an archery range, 14 horses, an amphitheater and a 6-to-1 student-to-teacher ratio, according to its website. Tuition starts at $24,900 for the 2019-2020 school year.

The lawsuit alleges the boy made the girl touch his genitals through his pants and forced her to perform oral sex by pushing her head down after he exposed his penis. Three school employees were “mere feet away” when the alleged assault happened, according to the lawsuit.

The girl was “quiet, withdrawn and looked like she had been crying” when her mother picked her up from the trip, the lawsuit reads. The teen told her mother she was tired and did not want to discuss the trip, covering her face with a jacket as they drove home silently, the lawsuit reads.

Over the next several months, the boy texted the girl an unsolicited photograph of his genitals, verbally bullied her and slapped her across the face in the school cafeteria after she told him to leave her alone, according to the girl.

At least one other student saw the incident in the cafeteria, the lawsuit states. Questioned by her mother about a red mark on her face, the girl said she “had an accident” at school.

The mother of another student found disturbing messages from the boy on her daughter’s phone, the lawsuit states. That parent told the mother of the student making the assault allegations about the messages and said she was concerned about the boy’s behavior toward other girls at Congressional.

On Oct. 23, 2017, the girl told her mother about the sexual and physical attacks and the photograph the boy sent, according to the lawsuit. The mother reported the attacks and inappropriate texts to Brenton Hinrichs, Congressional’s assistant head for academics, and declared she would not send her daughter to Congressional until the boy was removed from the school.

The next day, the girl and her mother met with Hinrichs and said the boy had been “physically assaulting her and verbally bullying her on a daily basis for months,” according to the lawsuit.

The teen making the assault allegations told Hinrichs about two other girls who said the boy touched them inappropriately, including one female student who complained to Hinrichs that the boy hit her, put his hands under her skirt and forcibly fondled her breasts, according to the lawsuit.

The suit states Hinrichs downplayed other allegations involving other students by telling the mother of the girl who said she was sexually assaulted that the boy only “touched their thighs” while at school.

According to the lawsuit, Hinrichs encouraged the mother to send her daughter to school “as if nothing happened.” He allegedly denied the mother’s request to have her daughter’s locker relocated away from the boy’s locker and rejected her appeals to keep the boy away from her daughter without adult supervision.

Hinrichs declined to comment about the allegations in the lawsuit through a representative for the school. He did not respond to messages sent to an email address for him found on Congressional’s website or to a letter requesting comment left Monday at a residence that public records identify as his home.

The mother said she decided to withdraw the girl and another daughter from classes after she “had heard nothing more” from the school. The girls’ last day at Congressional was Nov. 2, 2017, court papers say.

Hinrichs and Janet Marsh, who was Congressional’s head of school at the time, chose not to suspend or expel the boy, according to the lawsuit. It also alleged Hinrichs and Marsh “actively dissuaded” the girl and her mother from notifying the police.

Marsh declined to comment about the allegations in the lawsuit through a representative for the school.

Congressional School officials sent a message to community members Friday after receiving inquiries from The Post.

In the letter, Daniel Timm, chair of the school’s board of trustees, and Andrea Weiss, interim head of school, said Congressional commissioned Sheppard Mullin to determine whether the school “had failed in any way to properly safeguard our children, and whether it had failed to appropriately respond when these allegations were initially presented.”

“The lawsuit makes allegations that, if they were true, would be serious and unacceptable,” the letter reads. “We have confidence that the situation was handled appropriately and responsibly by all involved and that the evidence will bear this out.”

Broderick C. Dunn, an attorney for the girl and her mother, said he questioned the thoroughness of the school’s investigation, because his client was not asked to participate.

The girl and her mother filed a report about the alleged slap to the girl’s face on Oct. 29, 2017, with Fairfax County police. They filed a report with Arlington County Police the next day about the alleged sexual assault.

A Fairfax police spokeswoman confirmed a report was filed by the girl’s mother and said the case was closed. No charges were filed, police said.

Arlington police investigated the sexual battery allegations and presented the case to prosecutors, who declined to prosecute the case, a spokeswoman said.

The teen who is suing Congressional transferred schools but missed classes at the new school because of bouts of depression, anxiety, headaches and stomachaches, the lawsuit reads. She suffered chest pains, sleeplessness and weight loss, it says.

Tom Jackman contributed to this report.