Last month's Florida school shooting and the rash of copycat threats that followed in Minnesota and around the country has put the spotlight on how schools and law enforcement measure risks and respond.

Gov. Mark Dayton wants routine threat assessments of expelled students as part of a broader school safety package he announced Wednesday. His office cited media reports of at least 21 threats in Minnesota schools since the Parkland, Fla., shooting, where an expelled student killed 17 people.

"Threat assessment" became a priority for many school districts after the 1999 school shooting at Columbine High School in Littleton, Colo. A federal study that followed detailed how to evaluate threats and other student behaviors that may lead to violence; it was based on the U.S. Secret Service protocol for assessing dangers to public officials.

"The key steps are getting a good interview with the student ... looking at what is the student saying, what are the people that know the student [saying]. If there are other students that have come forward because of concerns, what are they saying?" said Virginia Nimmo, a retired Minnesota school psychologist who trains school administrators on threat assessments.

Threats or other red flags should be forwarded to a principal or to school mental health staff, she said. The evaluation could take less than a day or could extend for multiple days.

In the Bloomington Public Schools, officials determine whether a threat is substantial and if so, contact police, said district emergency management coordinator Rick Kaufman. School administrators and officers look for key information including motivation, means of carrying out the threat and evidence that the person intends to follow through, he added.

Schools around Minnesota are keen to improve security protocols following last month's shooting in Parkland, said Randy Johnson, director of the School Safety Center at the Minnesota Department of Public Safety.

He said the center's experts are booked until May for evaluations and trainings.

"I think schools are doing a very, very credible job in putting together their threat assessment processes, but there's always something new to learn," Johnson said.

For example, Johnson said schools are learning how to deal with social media threats. Social media messages can be anonymous, so Johnson said districts may need to rely more on law enforcement agencies' tools for finding a message's source.

The federal report cautions school officials against using student characteristics like personality traits or demographics to pick out would-be perpetrators.

"There is really no good profile that can say we should look at these particular groups of students as possible safety issues," Nimmo said.

Instead, she said schools should focus on the facts of a student's behavior.

Once immediate danger to the school or students is over, the work to help the students involved and prevent future problems continues, Nimmo added.

"It's not about a disciplinary action. It's about mental health and getting help to that individual and supporting them and supporting their family in what needs to happen next."