Spence became a school police officer after being fired from the Baltimore City Sheriff's Office in 2003 after he and another deputy Tasered a man they mistook for a bank robber. The footage - which has now gone viral - was secretly filmed by the kid's friend.
Officers were responding to a report of intruders and they moved two young men outside the building, he said.
The head of the city's school police force, Marshall Goodwin, has been placed on administrative leave, but some activists and elected officials say that's not enough.
Baltimore police are investigating a school police officer who was caught on camera hitting a young man inside a public school.
Karl Perry, the chief school supports officer, said, "I'm a parent, and I'm totally appalled at what I saw in that video".
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"You hope that's never your child, and that when your child goes to school, that child is respected and appreciated and that the people who take an oath to protect those children never turn around and do what that officer did to my client, " said his attorney, Lauren Geisser.
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Past year the city's school police department came under fire when a school police officer pleaded guilty to second degree assault following an altercation with three female students at a local middle school.
Geisser said she obtained a printout with the student's name on the school roster.
And State Sen. Bill Ferguson, a Democrat, has suggested Superintendent Gregory Thornton should be fired after school officials could not initially determine whether the teen in the video is a student. "He was injured and his family is traumatized by what happened", she said.
The officer is seen grabbing the student, and then wrapping his forearm around her neck.
"The boy had a right to be at the school where he was an enrolled student", she told CNN. "This is the right thing to do in a case like this and I have assigned S.I.R.T.to handle all aspects of this criminal investigation". "It has something to do with days that he was in school and when he was not", Parks told NBC News. "We're taking this very seriously".
In a statement Friday, the school system said it had scheduled an interview with the young man and his parents.
Melanie Shapiro, a juvenile public defender, said a school police officer using excessive force on a student is "not what we'd consider an isolated incident". Police also assigned an investigative liaison to assist school police. "But this incident was captured on video; there's no denying what happened".