Lockdown drills are a commonly practiced school emergency preparedness strategy, yet there is an alarming lack of empirical data to inform their use. In the current study, participants from a large, urban school district were surveyed at baseline, post-drill, and after receiving training on the newly implemented emergency response protocol and participating in a second drill, and the procedural integrity of the lockdowns was observed. Students and staff reported significantly increased perceptions of emergency preparedness following the training, although faculty reported these increases only for hazards not previously drilled. Classrooms increased by average of 27% in the correct implementation of lockdown procedures following the training (compared to the drill without training). Mastery was achieved for locking doors (89%), lights off (85%), and not responding to door knocks (91%), yet there was room for improvement in staying out of sight (71%). Additionally, continued participation in lockdown drills over the course of the study led to students, faculty, and staff expressing greater feelings of preparedness related to lockdowns, as well as other emergency scenarios (lockout, evacuation, shelter, and hold-in-place). Collectively, the findings of the present study highlight the importance of drills in fostering a culture of preparedness in schools.