We've seen school shootings that took the lives of five- and six-year-olds, as well as those that involved people in their early twenties (Timeline ). The days of the Columbine and Sandy Hook incidents will always be considered tragedies but also learning opportunities for the United States. In both of these cases, and in most other situations, the gunman entered the school with his weapon in hand, going unnoticed until the first shots were fired. danger to the school? Someone had to notice a change in the behavior of the two teenagers and say something. Klebold and Harris went on to kill twelve students and teachers, wound twenty-four others, and then take their own lives (School