The Denver school district said it is responding to an incident on a school bus in which district transportation personnel restrained a 6-year-old student Wednesday and called police.

The student has special needs. In a video taken by the girl’s mother when she arrived at the scene, the girl can be heard crying and screaming.

“Come on, honey,” the mother, Kristin Stark, says on the video. “Mommy’s here.”

“I’m not going to let you on the bus,” says a Denver Public Schools campus safety officer standing next to the bus door. “She can walk out to us.”

“Cecilia, you gotta come to me,” Stark says. “They won’t let me on the bus.”

Stark posted the video to social media.

“As you can see on the video, my daughter was absolutely terrified and hysterical when I got to her,” she wrote on Facebook. “And no one would allow me to help her gather her belongings from the bus, nor would they help her.”

Denver Public Schools said in a statement Thursday that its staff had reviewed video footage from a security camera inside the bus. The statement says the bus driver called 911 after bus staff “were unable to get the student back into a safety vest.”

While bus staff were waiting for police to arrive, at least one employee from the district’s transportation department showed up to help.

“After efforts to de-escalate the behavior of the student were unsuccessful, the transportation employee used a physical restraint with the student,” the district statement says.

The district said it is turning the bus security camera footage over to Denver police “for further investigation regarding the actions taken by the transportation employee.”

Stark has not seen the recording from the bus security camera. But she said her daughter told her she became upset when another student kicked her on his way off the bus.

Her daughter also said that an adult, who Stark assumed was a campus safety officer, held her face down on the floor of the bus with her arms behind her and his knee on her back. According to Stark, her daughter said, “He was holding me down and I couldn’t breathe.”

A district spokesperson confirmed it was a transportation employee, not a campus safety officer, who restrained the girl. There were no other students on the bus at the time.

By law, only armed campus safety officers are allowed to hold students face down on the ground in a “prone restraint” — and only under certain circumstances. Campus safety officers must be trained in restraint techniques and must have made a referral to law enforcement. Prone restraints can be dangerous because they can restrict a child’s ability to breathe.

Stark said her daughter has been diagnosed with oppositional defiant disorder and PTSD. She said she was waiting at home for her daughter when she got a call from the school district’s transportation department. The caller said Stark’s daughter was having behavioral issues on the bus, that the driver had pulled over at a certain intersection, and that Stark would have to pick her up there. The caller also said the police were on their way.

“I was really confused why they couldn’t deal with it and they were calling the police,” Stark said.

School districts are under increasing scrutiny for using police to deal with safety and discipline issues. Advocates say it can put children in what’s known as the school-to-prison pipeline.

In a recent incident in Florida, body camera footage shows a 6-year-old crying and saying “Help me!” as officers arrest her on suspicion of misdemeanor battery after a tantrum at school. In Pueblo in southern Colorado, school board members have asked hard questions about tickets issued for classroom misbehavior. Denver Public Schools banned the use of handcuffs on elementary school students last year after a family spoke out about their 7-year-old being handcuffed at school.

Stark doesn’t have a car, so she had to call a family member for a ride to where her daughter’s bus was pulled over. She estimates it was 40 minutes before she got there. When Stark arrived, she saw several Denver police officers, campus safety officers, and bus staff standing outside.

Stark said she gathered her daughter as quickly as she could and left. The incident was traumatizing, Stark said, and she didn’t want to prolong it.

“I felt so sick to my stomach,” Stark said. “I was worried about them hurting her.”

Stark said the incident has left her daughter shaken, and afraid of the police.

“She’s had traumas in her life, and this just adds to it,” Stark said.

The staff at her daughter’s school have been supportive, Stark said. On Thursday, she said they told her they’d be providing a special car service for her daughter so she won’t have to ride the bus.

While that’s getting set up, Stark said the school offered to pay for Uber service.