My son doesn't tell us a lot about what goes on at his high school (though we quiz him with what must be irritating diligence). But a few weeks ago, he volunteered that his class had practiced a "lockdown" operation. During this drill, the kids were taught code phrases, indicating that a shooter was at large in the school. When the code was announced on the loudspeaker, the teacher locked the doors, turned out the lights, and everybody sat on the floor in a corner. The object was to simulate the appearance of an empty classroom, so the shooter would pass by. My son reported that the class didn't seem worried or fearful. Kids were chatting quietly, relishing the break in the school day.

I was horrified by the idea that the school felt this kind of preparedness was necessary. It was different from the air-raid drills we practiced in elementary school during the Cold War. We hid under our desks on the theory that Russian bombs couldn't penetrate a rickety wooden table with an inkwell-hole in the corner. But in those years, the enemy was outside, some Soviet apparatchik in an ill-fitting suit. Today, the shooter is just as likely to be someone my kid knows, someone from the lunchroom or math class. Someone crouching next to him as he learns the code words for danger.

This week in Santee, California, the someone was a 15-year-old boy, a kid with friends and a smile on his face who sprayed bullets into his schoolmates, fatally wounding two of them. The boy's mother, who lives eight states away, who last spoke to him "earlier this year," says she never detected any real moodiness in her son. His friends heard his threats but thought he was kidding. But there is no such thing as a harmless teenage fantasy anymore.

It's happened in our town too--a pleasant suburb across the country from Santee, dozing today like a Currier & Ives print under its frosting of snow. Last year, two boys from our high school set themselves up as gun dealers, using a falsified license they obtained over the Internet. A UPS employee, delivering a parcel with a gun-store label to a private house, grew suspicious when the only person home to accept the package was a teenage boy. The police were alerted and made an arrest. The kids were suspended, but the local paper never reported the outcome. Were they jailed? Are they back in class? And what exactly were they planning to do with those guns?

It's a relief that today is a snow day, and school is out. A day off from worry, a day of innocence, of sipping hot chocolate and shoveling the walk. But inevitably, the kids will go back to school. Every morning when my son leaves for school, I squeeze his shoulder and wish him a great day. He's too big to hug and hates when I muss his hair. But I've just got to touch him, as if that touch could place some protective shield around his 6'3" frame.

He doesn't know it, but that squeeze is secretly a prayer. That he drive safely. That he not get hurt on the basketball court. And that some angry, outcast kid not gain access to a gun and take out his hurt and rage on his school. Every parent I know will be saying the same prayer of protection. Let the enemy pass by.