In 1999, the year of the shootings at Columbine High School in Colorado, Heath E. Morrison was a middle school principal in Maryland, shocked by what he and his colleagues saw as a terrible but unique episode. “There was this intense desire not to overreact,” said Mr. Morrison, who is now superintendent of the Charlotte-Mecklenburg school district in North Carolina.

Since then, Mr. Morrison has come to view schools as much more dangerous places. In the wake of the Newtown, Conn., shootings last week, he finds himself contemplating heightened measures to protect students, including increasing the number of security officers in schools who carry their own guns.

“We are a country that has too much violence and too many ways to have people hurt or killed and not enough access to mental health services,” Mr. Morrison said. “So if there was an ability to put an armed security officer in every school, I would have to seriously consider it.”

Charlotte-Mecklenburg already stations armed security guards at the district’s 28 high schools, though not at its 88 elementary schools. Across the country, some 23,200 schools — about one-third of all public schools — had armed security staff in the 2009-10 school year, the most recent year for which data are available.