The physical altercation played out inside the school's cafeteria on Monday.
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School officials have said they are taking this matter seriously and the school staffer has been removed while CPS investigates.
Cell phone video appears to show the staff member with his hand around the student's neck before the teenager is slammed to the floor.
Student Bruce Guzman was there.
"It's surprising to see that. It was unexpected," Guzman said. "I was just sitting and all of a sudden see a security guard dropping a student. I kind of ignored it so I won't be apart of it. "
The school's principal sent a letter to parents informing them that an investigation has been initiated by the Office of Student Protections and Title IX.
He also said the employee has been removed as the investigation continues, but would't elaborate on what role that staff member holds in the school.
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He added that the "family of the impacted student has been notified and supports are available to the student."
On Wednesday morning, students at the Northwest Side high school were grappling with the fallout.
"Being a senior, it's not surprising. It's stuff that does commonly happen here," Bryana Navarro said.
"I think it was kind of wrong only because the kid did get really hurt," said junior Claudia Deleon.
"The student was being aggressive. I felt like the security guard did his job actually. He did what he had to do," said sophomore Anthony Bahena.
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The extent of the student's injuries are unknown and school officials are not elaborating on what led up to the scuffle.
Some parents are looking for more details.
"It's not fair, you know, for him to have put his hands on the teenager, or vice versa, you know, but there's always a back story to that," Maria Navarro said. "You don't want your child to go through that but I understand there's sometimes situations you can't help it. It's bad but hopefully it gets resolved."
The staffer's employment will be based on the outcome of the investigation.