This month’s cover story is about security in K-12 schools, and it is all too apt. As we were going to print in early October, three incidents had just occurred.

One involved a gunman with no criminal record who shot 11 girls at an Amish school in Nickel Mines, Pennsylanvia; five had died at press time. Another involved a 53-year-old with a history of petty crime who entered Platte Canyon High School in Bailey, Colorado. He took six girls hostage, sexually assaulting some and fatally shooting one.

The other incident occurred at Weston High School in Cazenovia, Wisconsin, a community with only 300 residents. A student walked in and fatally shot the principal. In that case, the news reports noted that the school had no metal detectors or security guard. Why should it, said one commentator, given that it was such a small community.

On its face, that may sound like a reasonable conclusion. Statistically, despite these three shootings, the chance of any one child getting fatally shot at school is about one in one million.

But when people conclude from those statistics that security is not needed, they are making a common error. They forget that in addition to the risk level, they must consider the value of the assets being protected and the consequence of those assets being “lost.”

In the case of our schools, the assets are the children, and their value is truly incalculable, as is the consequence of their being harmed. In the security vernacular—as readers of this magazine well know—that’s called a low-probability, high-consequence event. In such cases, it’s unacceptable to just roll the dice and play the odds. Schools have a responsibility to act.

The Broward County School District in Florida has supplemented its funds with two $500,000 government grants to implement a range of programs to protect its young charges—including the computerized visitor management system detailed in our story.

Schools without gifted grant writers may not be able to get state-of-the art systems. But security doesn’t have to bust the budget. Even just raising the level of awareness among students and teachers and ensuring that kids and parents know to report troubling behavior can save lives.

That was the case at East High School in Green Bay, Wisconsin, in September, when three teenage boys were turned in by a classmate who had heard they planned a Columbine-like attack. The boys were found to have a cache of weapons and suicide notes. According to a CNN report, “School Superintendent Dan Nerad credited school staff and their relationships with students for allowing them to learn of the situation and immediately get the school resource officer involved.”

When the current spate of shootings fades from the headlines, we must not let complacency return. As schools evaluate the need for security, they should remember the most important statistic: Every child is one in a million.