Parents of students at the school say they're concerned that he was able to get in without anyone noticing.
"That's the scary thing. When I heard that last night I was like what! I didn't know," Said Mary Olivarez, whose son attends Cooper.
Olivarez says her son was right outside the cafeteria when the fight started. She's afraid it could have been much worse.
"You never know he could have a weapon. Or he could have something that we don't even know whats going to happen in there. And that was the biggest shock for me because my kid was there," Said Olivarez.
According to Abilene Police, the juvenile was confronting a student in the lunchroom.
When he was asked to leave, he refused.
That's when the school resource officer was called.
"The officer, I think he was right to get him out of the school because he wasn't supposed to be there. I think he did the right thing because, what if hes got a gun and he starts shooting people," Said David Castenada, who was picking up his granddaughter at Cooper.
AISD officials declined to speak on camera but did release this statement:
"While we regret that an unauthorized video taken on our campus is being published in the media, we have complete confidence in our school personnel and City police in keeping our campuses safe. That includes efforts such as this incident where it was necessary to contend with a former student trespassing to confront current students, then refusing to leave when asked."
Still, some parents think extra precautions need to be put in place.
"They need to enforce the rules a little stricter," Said Marlin Hines, as he was picking up his granddaughter.
"They could have cameras. Some schools have cameras," Said Olivarez.