Jimmy Jenkins/KJZZ

Phoenix students gather at the Arizona Capitol to protest gun violence in schools on Apr. 20, 2018.

April 20 is the anniversary of the mass shooting at Columbine High School in Colorado, a turning point in the conversation about school safety. But we’re still experiencing school shootings — and nationwide protests.

So what, if anything, has changed in the last two decades?

David Osher is vice president and Institute Fellow at the American Institutes for Research and an expert on violence prevention and school safety and he said, since before Columbine, there have been two different responses to school shootings in this country. First, a focus on security, things like metal detectors and getting more police into schools.

The other, a focus on prevention that includes security, but also looks at things like social-emotional learning, positive behavioral supports and mental health services as a way of heading off problems.

He said there has been some progress made in terms of policy since Columbine and even since the shooting in Newtown, Connecticut. But, there has never been enough money for those programs to scale them up or sustain it, according to Osher.

At the same time, he said, the security approach has not worked either. Shootings still happen in schools that have School Resource Officers.

Osher said it is important in thinking about prevention here is the idea of creating a safe school climate.