Students escorted to a school bus at STEM School Highlands Ranch after the shooting. Photo: Hyoung Chang/MediaNews Group/The Denver Post via Getty Images

For some parents, their child’s back-to-school shopping list has expanded beyond crayons, glue, and pencils. With the increased frequency of mass shootings we’ve seen in 2018 and 2019, their shopping list is including bullet-resistant backpacks. Sales of bullet-resistant backpacks have increased by nearly 200% in the past two years.

This measure, among many others (e.g., arming teachers) advocated by lawmakers, will not stop school shootings. They are measures used after the gunfire has begun. We need a system or program that prevents a person of concern from entering a school with the intent to injure others. A lot of attention is being placed on gun control. I see this as an entirely separate issue. We need a system that will stop someone with a gun, knife, bomb, or club. I want to give you insight into how these tragic events are occurring and how we can stop them from ever happening in the first place.

I am a former member of a county-wide school threat assessment team. In 180 days of school, I performed 125 behavioral threat assessments. I train school staff and police officers all over the United States on how to identify an individual on a path to violence, determine their level of risk, and then how to manage them. The knowledge of how to identify concerning behavior is a skill everyone should have, not just police officers. I will share it with you here.

The first thing you need to know about people who have committed these violent acts in schools, workplaces, or in public areas is they didn’t just snap. They didn’t wake up one day and say, “I’m going to shoot everyone at my school.” They planned the attack, sometimes weeks, months, and in some cases, years in advance. We call this “targeted violence.” Their planning and p ...