Most schools have no need but Detroit area schools have them and the gang bangers still manage to kill each other.
In addition to security officers, I think they also have metal detectors.
Two reports I heard on Channel 7 news a number of years ago:
1. News babe reported on a student who was caught bringing an assault weapon into one of the Detroit high schools. Several days later, a follow up report said it was a shotgun.
2. Also a few years ago, Channel 4's Bill Proctor reported on a shooting in Detroit. He said, and I quote: "Police are looking for a .357 Smith and Wesson Glock Pistol"...........no lie!