On Nov. 30, 11 people were shot, four fatally, at Oxford High School, about 45 miles north of Detroit. The crime scene investigation understandably closed the school for a week. Threats of copycat violence then closed the school again.

Shooting threats typically increase after a high-profile school shooting because the public is on high alert and violence is socially contagious. Michigan's online threat reporting system received more than 3,000 anonymous tips after the Oxford shooting. Many threats were hoaxes or not credible, but officials closed schools anyway out of an abundance of caution.

The problem was not limited to Michigan. Over 500 school systems across the country, including Philadelphia, Houston, Oakland, North Texas, and Bellingham, Wash., closed owing to shooting threats in recent weeks. In the tiny Cuba Independent School District, 85 miles north of Albuquerque, school officials ended fall semester early following threats posted on Instagram.

And on Dec. 17, schools nationwide, including in Minnesota, closed in response to an anonymous threat on TikTok warning against students attending class. The viral trend encouraged students to participate in "National Shoot Up Your School Day."

School closures offer no long-term solution to school violence. Our research shows that the lead-up to a school shooting is years of trauma, isolation and hopelessness, and months of preparation.

Would a student who has assembled a hit list and an arsenal of "ghost guns" simply give up on the plan of attack because school was closed that day?

School closures also are expensive. The cumulative economic cost of shuttering schools nationwide last week is billions of taxpayer dollars. That's on top of the costs to frustrated parents missing work to home-school their children and anxious children missing valuable classroom learning time to process the prospect of potentially being shot and killed at school.

The problem is schools are already overburdened and they don't know what more they can do. All schooling is local. Responses to threats vary and rarely do they follow best practices in threat assessment and crisis response. Many school systems struggle to buy textbooks and tablets. Absent the resources needed to conduct a formal assessment and make an intervention plan, they have no choice but to close their doors.

Our research shows school shooters regularly post threats and communicate intent to do harm in advance, so the warning signs must be taken seriously. Any school closure must be followed up with vigilance from parents (including safe storage of firearms), support from school staff, and appropriate intervention from police and community partners.

On Dec. 17, we hosted a webinar for school leaders to help them prepare for the next threat of school violence. It all starts with creating a culture of care that ensures every child has at least one trusted adult in their lives and is empowered to say something if they see or hear something.

Our research with school shooters shows that many real threats are a cry for help and we must recognize them as such. The Department of Public Safety Bureau of Criminal Apprehension (BCA) has a new app for reporting planned or threatened violence at Minnesota schools called See It, Say It, Send It. The BCA will triage any tips that come in and either notify local law enforcement or work with the Minnesota School Safety Center, the Minnesota Department of Education, and with schools to determine the appropriate response.

See It, Say It, Send It was developed with a one-time federal grant, but it will need ongoing investment to keep up with rising demand — over 40,000 Minnesotans have downloaded it already. At the same time, schools need funding to set up dedicated "crisis response teams" made up of educators, public safety experts and mental health practitioners who can help assess incoming threats in the context of students' development and unique circumstances. These teams coordinate restorative interventions for students in crisis and follow up to make sure they are working.

The financial burden of this work need not fall on each individual school or district. When there is a national trend in online threats and every school shooting reverberates around schools nationwide, the federal government has an obligation to resource a solution. There is presently no clear national standard or guidance for evaluating online threats nor federal appropriations for building a crisis response team.

An overused phrase — an ounce of prevention is worth a pound of cure — rings true. Spending a few thousand dollars on threat mitigation could save millions in just one day. Closing schools in response to each and every violent meme posted on social media is unaffordable — a knee-jerk reaction when many threats are just impulsive teenagers trying to force a day off.

But the cost of inaction — the next Oxford, Parkland or the tragically long list of American school shootings — is too high a price to bear.

David Riedman is the co-creator of the K-12 School Shooting Database at the Naval Postgraduate School. James Densley is a professor of criminal justice at Metropolitan State University. Jillian Peterson is a professor of criminology and criminal justice at Hamline University. Densley and Peterson are co-founders of the Violence Project and co-authors of "The Violence Project: How to Stop a Mass Shooting Epidemic."