Valentine’s Day brought another sadly familiar hail of deadly, semi-automatic gunfire at a school, this time at Marjory Stoneman Douglas High School in Parkland, Florida. The alleged shooter, a former student, killed 17 people.

Sobering scenes of weeping parents and children and students evacuating their school in a line, hands on the shoulders of the classmate in front of them, again stoked the heated national debate about mass killings at schools in the United States. Speaking on the Senate floor Wednesday, Sen. Chris Murphy of Connecticut – the scene of the deadly 2012 Sandy Hook Elementary School shooting – reminded his colleagues that “this happens nowhere else other than the United States of America.”

University of Virginia forensic clinical psychologist Dewey Cornell is the architect of the Virginia Student Threat Assessment Guidelines, which are widely adopted by schools in Virginia and help teachers and administrators assess and address lower-level threats like bullying and teasing before they escalate to deadly levels.

Cornell, whose expertise in threat assessment has been featured on the “PBS News Hour,” The Washington Post, Vanity Fair and elsewhere, participated in a Facebook Live session on Thursday to discuss school safety.

One of his greatest takeaways was that there is a huge imbalance in the resources allotted to school security and those given to violence prevention. A big believer in the need to support school security, Cornell said “prevention has to start before there is a gunman at your door.”

“If you are thinking about ‘What if we have a gunman?’ that’s fine, but that’s not prevention,” he said. Think of the people who are troubled, those who are distressed and need help, Cornell added. The armored vehicles that were dispatched to Marjory Stoneman Douglas High School Wednesday could fund “many, many schools’ professional development and school counseling resources to help kids.”

After the Sandy Hook massacre and the shootings at Virginia Tech, Virginia became the first state to require threat assessment teams in every public school, partnering with Cornell, a professor in UVA’s Curry School of Education, who has been studying school safety for more than 26 years.

A recent study from Cornell found the vast majority of threats made in Virginia public schools were judged to be not serious. Schools want to avoid both overreacting to the student threats that are not serious and underreacting to the threats that are, he said.

Another of his studies found that Virginia public schools that employ Cornell’s threat assessment technique had smaller racial disparities in their long-term suspension rates and that successful threat assessment was associated with lower rates of out-of-school suspension overall.