This is backwards
If you look at anyone who commits a mass killing I suspect you will discover that the vast majority of them if not 100% all have "issue" as kids. But if you take that same issue that Adam Lanza had (Sandy Hook) or Nikolas Cruz had (Parkland) you may find 100,000 others who had the same issue and didn't go out and commit mass murder.
You don't change a school policy and basic law of protecting minors at school by keeping those records private because 1 out of 100,000. You will damage, defame, and slander 100,000 kids in the thought that you will get that one mass murderer? On the contrary you will probably create 10 more for every 1 we have right now.
If a kid threatens to harm others then of course, teachers are mandated to report that and make that report the same day they hear it. Once the report is made it is referred to the proper authorities, and if the report alleges criminal behavior it is referred to the police. Anyone who works in schools knows this.
However, this process is the most abused process in the school system. In order to encourage people to make reports when they aren't sure everything is anonymous. As a result half of these reports are just people trying to slander and harm others.