Since the beginning of the school year, there have been 25 shootings at or near schools nationwide.
Seven of the shootings -- three in the last week alone -- have been fatal.
With the exception of a 15-year-old Wisconsin teenager who allegedly killed a high school principal at school last Friday, the gunmen in these recent attacks appear to be getting older.
The killings began Aug. 24 when a 27-year-old man walked into an elementary school in Essex, Vt., killed two teachers and wounded two other people before turning the gun on himself.
He survived his injuries.
Last week, a 53-year-old homeless man molested several girls before killing one girl and himself in Bailey, Colo.
On Monday, a 32-year-old milk truck driver lined Amish schoolchildren up against the blackboard of their one-room schoolhouse and shot five young girls before turning the gun on himself. Three died in the schoolhouse.
Experts say the shootings could be copycats of one another.
"Today's tragedy becomes the event that plants the seed for tomorrow's crisis," said Ronald Stephens of the National School Safety Center.
The recent rash of shootings evokes the same painful images like those seen during the late 1990s' spate of school killings, most memorably at Columbine High School in Littleton, Colo., in 1999.
Since the Columbine massacre, some experts say, the country has not done much to protect schools as some might think.
The overwhelming majority of schools in the United States do not have security cameras or metal detectors.
Fewer than half have security personnel on campus.
"The common refrain over and over is we never thought it would happen here, and it is when we have 'it can't happen here mentality,' that is when we are most vulnerable," said Kenneth Trump of National School Safety and Security Services.
Between 1992 and 2002, 462 people -- including students and faculty -- were killed at schools across the country.
Most would agree that when it comes to children being killed at school, even one is too many.