There is an ongoing debate in this country whether law-abiding concealed handgun permit holders should be allowed to carry concealed weapons on school campuses - elementary through the university level. Never mind that those who take the effort to get the training and background checks and spend the money to get the permit are far less likely to engage in violent crimes than the rest of the general population. (The statistic from Florida is that permit holders are 300 times less likely to commit a violent crime with a firearm.)
In Israel, this debate has been over for decades, and their decision works. In a January 25th article, IsraelInsider reported that two armed Palestinian terrorists broke into an Israeli high school and attempted to take hostages. If this happened in the US, the result would be catastrophic. Who knows how many would be shot, blown up, kidnapped or traumatized. In Israel, the result is two dead terrorists killed by armed counselors, and minor injuries suffered by the two counselors who resisted. By the time the authorities were notified and arrived on scene, the danger was over and the kids were safe.
Psychopaths, terrorists, and criminals of all types need to know that schools (and malls, and churchs, and everywhere else) are unsafe places - for them. Children should know that those responsible for caring for them are capable of protecting them, and that school is a safe place where they can focus on reading, writing, 'rithmatic, not wondering what unstoppable threat is coming next through the classroom door.