I recall posting here before my stance on this - one instigating factor in school shootings is that the victims are essentially guaranteed to be defenseless by law.
The “wackos” that perpetrate such acts aren’t entirely irrational - motivated by revenge or notoriety they generally seek to kill as many folks as possible and figure that a place where people can’t defend themselves is such a place. Most debates focus on the “shooting back” aspect, but I believe the knowledge that the victims may not, in fact, be quite defenseless is a solid deterrent to a would-be mass murderer regardless of whether firearms are actually carried or not.
The other major factor is that school (and work) are stressful places where people spend a lot of time, it’s relatively easy for an unstable person to “go off the rails” for some perceived (or real) social problem. Young people are particularly unstable since they’re still growing up, which exacerbates the issue.
While I agree that relaxing CCW restrictions in schools would probably help with events like the one at Virginia Tech, a bit more emphasis on psychological support for students with problems would go a long way to cover the suicide issue as well, which is a big one for young adults.
Obligatory CDC link follows, which has a 216 page paper (free downloadable PDF) on what they feel are best practices for resolving the problem of youth violence:
Center for Disease Control - Youth Violence Prevention
In a nutshell, they focus on effective conflict resolution and communication skills, mentoring, identifying problems early, and so on - understating rather eloquently: “…when adolescents are faced with social situations for which they are unprepared for emotionally and cognitively, they may respond with aggression…”.
These are essential life lessons to learn in their own right, I’m not sure why they’re not a more substantial part of the school curriculum already. Many folks pick this stuff up naturally through social interaction, but there are many who do not with ramifications well through adulthood.