KINGSTON (CBS) – The single digital snapshot, taken by a student cowering in the dark, looks more ominous than it really is.

Last week, more than two dozen SWAT team members descended on Silver Lake Regional Middle and High Schools.

Their weapons were drawn, but not loaded. They ran through the building, simulating their approach to a scenario in which a shooter or shooters were also inside.

It’s called a “Code Yellow” and is meant to be a drill that prepares teachers and students for an unthinkable – but possible – reality.

“We’re looking for it to be as realistic as possible,” explains Silver Laker Superintendent of Schools John Tuffy. “The doors are locked, the lights are turned off, and the students are asked to go to a safe place in the room, an area where you can’t be seen through a window or a door.”

Such drills have been going on for years, but in a post-Sandy Hook educational environment, they have taken on a chilling importance.

“They came in with guns; it was sort of scary I guess,” explains Silver Lake eleventh-grader Nick Dwyer. He says in his room, “everyone in the class just dropped to the ground” and largely remained calm though the 30-minute exercise. It was only after it was complete, though, that everyone knew for sure it was only a drill.

Notes from the school went home to moms and dads that day; some called to complain immediately. Angry parents said their children were distressed by the experience. But most, according to school administrators, seem accept this is something that just has to happen.

“It’s sad but in another essence it’s good though, because you never know what’s going to happen,” said Silver Lake parent Wayne Reissfelder.

“I think it just gives the kids a better idea of where they have to go when and if that ever happens,” offered Pam Malley, whose daughter goes to Silver Lake. “They need to do that in this day and age, which is sad.”