In the spring of 1999,12 students and a teacher were killed by two gun-toting teenage boys at Columbine High School in Littleton, Colo., making school safety and security an overnight priority in communities across the nation. Eight years later, a second and even more deadly incident on the campus of the Virginia Polytechnic Institute and State University, where a student shot and killed 32 people, brought a renewed wave of concern and attention to security. But these two largest U.S. school shootings to date were by no means isolated incidents, as 60 similar events at American schools were reported between October 2007 and February 2008, according to a 2008 U.S. News & World Report article. ?Columbine was the undisputed impetus for a whole new focus on school security, and it had a major influence on the construction of new school buildings and the renovation of existing ones,? says Judy Marks, director of the National Clearinghouse for Educational Facilities, a program of the National Institute of Building Sciences that provides information on designing, building and maintaining safe, healthy, high-performing schools.