It depends on the school and the shooter. In many cases, the high school will have far more students and faculty, meaning more possible victims. However, high schools are better equipped to deal with the issue as the students have almost certainly been prepared with drills and have been far more exposed to news stories of such shootings. Depending on the location there is often a police officer on or around the campus, and teachers trained specifically for these situations. Also, school layouts are important. Many larger schools are broken into wings that can be locked down in times of emergency, where as smaller schools are far more accessible. We also have to consider the shooter. My guess is that someone looking to shoot up a high school is probably going to be focused on a select individual or group of individuals as a result of bullying or emotional dissidence. If the shooter is of a matured age, they're going elementary school looking to cause the most terror possible. I feel as though the elementary school shooter is acting in a more sociopathic manner than the high school shooter who may be acting vindictively. That being considered, those acting on a whim of reactionary aggression are more likely to recognize the fault in their judgment and recoil, where as those acting from a more sociopathic basis don't actually care about faults in their judgment. I think all things considered, if the shooter is of a matured age, the elementary school is the option I would seek. Also, as a comment towards the other replies to this thread, I don't personally believe we can weigh the value of a human life over another based solely on age when none of the age groups considered are fully matured already. I think it's fair to say that a child should be saved over an elderly person, but when the age gap is so small, I would argue this sort of appraisal falls short of being very meaningful.