Locked doors are a critical factor in reducing school shooting casualties, study finds

SAN MARCOS, Texas—Locked doors and consistent access control practices play a key role in reducing casualties during school shootings, according to new research from Texas State University’s Advanced Law Enforcement Rapid Response Training (ALERRT) Center.

The report, “The Role of Locked Doors and Access Control in School-Based Active Shooter Events,” was conducted in partnership with the Security Industry Association (SIA) and analyzes 54 school-based active shooter incidents between 2000 and 2025, resulting in 324 total victims. Researchers examined how attackers entered and moved through school buildings, along with the effectiveness of door locks, lockdown procedures and other access control measures.

Among the study’s findings, 69% of perpetrators gained entry through an unsecured door, while nearly two-thirds (61.7%) of doors involved in incidents were found unlocked or intentionally propped open. No functioning locked door in the dataset was successfully breached by defeating its locking mechanism.

The research also found that casualty likelihood was approximately three times higher when doors were unsecured compared to secured doors. Nearly half of attacks began in hallways or outside areas, underscoring vulnerabilities in common spaces such as corridors, courtyards and entry points.

More than half (55.6%) of the incidents occurred in high schools, compared with 18.5% in elementary schools and 16.7% in middle schools. Attacker profiles varied by school type. In middle and high schools, most incidents involved insiders, with current students accounting for 88.9% of shooters in middle schools and 83.3% in high schools. In elementary school incidents, all attackers were outsiders.

While 75.9% of incidents involved a lockdown procedure, the study found that in some cases lockdowns were not initiated until after the attacks had effectively concluded, limiting their impact.

“The most common way an attacker entered a space was not by defeating a lock - it was by walking through a door that should have been locked but wasn’t,” said Hunter Martaindale, Ph.D., director of research at the ALERRT Center and lead author of the report.

The study also highlighted the importance of delay during an active shooter event. Even when attackers eventually breached entry points, locked classroom doors often slowed movement long enough for occupants to initiate lockdowns, notifications to spread and law enforcement to respond.

The report outlines eight evidence-based policy recommendations, including ensuring every classroom door has a functional lock that can be engaged from inside the room, addressing vulnerabilities in glass features around doors, maintaining consistent security procedures and prioritizing routine maintenance and repairs. The researchers also raised concerns about aftermarket door barricade devices, noting they can introduce safety risks and operational complications.

The independent research was supported by a grant from the SIA Endowment Program. SIA said the findings are intended to help inform school administrators, security professionals, law enforcement and policymakers as they evaluate school safety best practices.

SIA will host a webinar on June 18 featuring Martaindale and members of the ALERRT Center to discuss the research findings and their implications for school security. RSVP here.

Access the full research report here.

Photo courtesy of Security Industry Association