FORT LAUDERDALE, Fla. -- Fort Lauderdale police are investigating a sexual assault involving an 11-year-old girl on school grounds and why the school waited to report it.

A teacher at William Dandy Middle School claims she saw two 13-year-old boys sexually assault an 11-year-old girl near the school's parking lot during class time on Wednesday, Dec. 19. The victim and the accused are all special-needs students.

The teacher who witnessed the assault alerted security immediately, but nothing was done, so the next day she told the interim principal and wrote a statement documenting the assault. The assistant principal and the victim's teacher allegedly handled the incident internally.

It wasn't until Friday, two days later, that the incident was reported to police, and only after a school resource officer overheard the witness discussing the assault.

"Our superintendent … is holding a video conference with all principals to inform them of the reporting requirement when it comes to any kind of activity like this that may be occurring, including to the state child abuse hot line," Broward County Public Schools spokesman Keith Bromery said.

According to the police report, in which many details are redacted, the victim's mother was told "she pulled her pants down" and when she responded to the school, at no time was she advised of the sex allegation.

The victim's mother told Local 10 a Fort Lauderdale police detective informed her that two boys had sex with her daughter.

"I told her, 'No way. It can't be,'" the victim's mother said.

The victim's aunt claims the school engaged in a "massive cover-up."

"They changed her clothes," the victim's aunt said. "Where's the clothes that they changed? Nobody can say where the clothes are or who changed the clothes."

The victim's mother said her daughter hasn't been the same since the incident.

"She's quiet now," the victim's mother said. "She's not playing or laughing, you know, like her usual self."

Bromery said the school district is taking the allegations seriously.

"We are responsible for the care of children that are put in our charge," Bromery said.