http://en.wikipedia.org/wiki/List_of_school_shootings_in_the_United_States
School shooting =!= mass murders who happened in schools.
Also mass murder spree didnt always happen in schools.
(most of the events related in this link have only 1 or 2 victims, hardly mass murders)
We can compare numbers and frequency and damages done by mass murders relative to the soil it happened on, but the fact is it happens world-wide, with or without strict gun control.
I still agree with HESKEY, we can reduce the numbers of victims. The 2nd amendment has a responsability in the grand scheme of things, but it would be a mistake to say it is the only parameter in question.
There is a lot of things to do in favor of less gun victims without modifying the US constitution.