Eight girls from a Bay Area middle school were arrested this week after police say they plotted and attacked another student.

The eight students from Sinaloa Middle School, ranging from 12 to 14 years old, were arrested Tuesday and booked into Marin County Juvenile Hall on suspicion of conspiracy and felony assault, according to the Novato Police Department.

On May 24, the group gathered after lunchtime at the school and planned to assault another student, authorities said.

When they attacked, other children started recording it on their phones and egged on the fight, police said. One student tried to intervene but was also assaulted; both students attacked were hospitalized with moderate injuries.

Video broadcast on KTVU-TV showed a girl on the ground being punched and kicked by three other students.

Novato police, along with the Novato Unified School District and Sinaloa Middle School administrators, launched an investigation and identified the group responsible for the attack, police said.

Students knew the fight was going to happen the day before it occurred, according to an email sent to parents obtained by the TV station.

“This resulted in a very large stampede of our students (several hundreds of them) rushing around the campus to seek out the fight to watch it happen,” school officials wrote. “This mob grew in size as they ran through the campus, causing some students to fall and literally be run over by others.”

District officials didn’t immediately respond to a request for comment Friday morning.

School principal Christy Stocker and other district administrators spoke with more than 200 parents from the school on Tuesday, according to the Marin Independent Journal. Parents of the students who were injured said that they were doing OK physically but emotionally shaken.

“This was a horrific attack,” district superintendent Tracy Smith said during the meeting, according to the outlet. “It’s completely unacceptable and will not be tolerated.”

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This story originally appeared in Los Angeles Times.