Have You Been Through a School Lockdown? Tell Us About Your Experience

Agence France-Presse â€" Getty Images In this photograph taken from a video by KCNC-TV, Arapahoe High students in Centennial, Colo., lined up to be checked by police officers at a track after the Dec. 13 shooting at the school.

This month, when an 18-year-old student walked into Arapahoe High School in Colorado with a pump-action shotgun and began shooting, teachers and students and administrators knew almost immediately how to respond. Classroom doors slammed shut. Students huddled in the corners and stayed quiet. A resource officer inside the school sprang to action. Nearby, other schools locked down until they knew whether they, too, faced any threat.

For years, school districts in suburban Colorado and around the country have been performing lockdown drills in anticipation of just such a moment. Since the attacks at Columbine High School in 1999, active-gunman drills have become as much a part of a school’s emergency planning as tornado and fire drills once were.

Are you a parent, teacher or student who has experienced these emergency lockdowns first-hand, whether because of a real threat or a simple false alarm? What happened? How did students and teachers react? Did the planning pay off, or were there problems in the implementation?

Please post a comment below. I may follow up with you to hear more about your story. Or you can email me at jack.healy@nytimes.com.