Not sure what the percentages are, but with hundreds of thousands of schools in this country and only a few schools have experienced shootings, the percentage is very low. While even one school shooting is tragic and sad, thankfully, they are rare. Children most likely will be traumatized by many other things in their schools much more impactful since most will never be faced with this. Preparing an exercise such as this without notifying students and parents is just incredible and hard to believe. The children will be traumatized no doubt by something that they likely would never have had to face. Seems to me arming a few responsible adults to protect the children would be much more sensible than scaring children enacting a situation in which they would have no control. What good is training them when there is no chance they can outrun a bullet.