Sandy Hook shooting: Are schools in Lockdown America overreacting?
13 December 2013 Last updated at 01:28 GMT
The terms "lockdown" and "shelter in place" were once only used during prison riots and in emergency manuals. Today they are commonly used in US schools.
The mass shooting at Sandy Hook Elementary School in Connecticut on 14 December 2012 sparked a new debate about how to keep children safe - and whether lockdowns are the best response to a threat at or nearby a school.
There is no official database on the number of lockdowns, making it difficult to track whether they are on the increase. The BBC found news reports of at least 130 separate incidents where schools or college campuses were "locked down" in the month between 9 November and 9 December.
Are these lockdowns evidence that schools are overreacting (or acting out of "abundance of caution") or proof they are better prepared for the worst? David Botti reports.
Additional images: Google Maps, Getty Images, Thinkstock, Associated Press, and AP/Newtown Bee, Shannon Hicks