Security is a million miles tighter than it was 20 years ago. When I was in high school, I had different days off than the local public school, so I used to drop by and have lunch in their cafeteria with my public school friends from time to time. No one ever took the slightest bit of notice.
There is no way that I could do that now. None at all. (And not just because I'm 40.)
At my kids' schools, there are electronic locks and funneled traffic. How do these folks still get in, and what -- besides armed guards and barbed wire and machine gun nests -- can we do to stop them?