Have you seen these Breitbart pieces?
School Obama's Daughters Attend Has 11 Armed Guards
If you dismiss this by saying, "Of course they have armed guards -- they get Secret Service protection," then you've missed the larger point.
The larger point is that this is standard operating procedure for the school, period. And this is the reason people like NBC's David Gregory send their kids to Sidwell, they know their kids will be protected from the carnage that befell kids at a school where armed guards weren't used (and weren't even allowed).
D.C. School (Sidwell Friends) Posts Job Opening for Police Officer
Before the horrific crime at Sandy Hook Elementary even took place, some schools in our nation were already putting armed security and police officers on their campuses. As a matter of fact, one such school—Sidwell Friends School in Washington, DC—posted a job opening for a night shift police officer on Nov. 28, so they could have protection around the clock.
According to the posting, the position "is the overnight/midnight shift," and they made it clear that candidates would have to provide copies of their training credentials, SPO license, and professional references.
http://www.sidwell.edu/news/article/index.aspx?linkid=32603&moduleid=379
http://theambientvoices.blogspot.com/2012/05/ronald-security-sidwell-friends-school.html