Editor's Note: Dr. Frank Ochberg is Clinical Professor of Psychiatry at Michigan State University and former Associate Director of the National Institute of Mental Health.

By Frank Ochberg - Special to CNN

School shootings are far more frequent in America than in other countries, although terrible massacres have occurred in Russia, Israel, and several European nations. In the high-crime neighborhoods of inner cities, school turf is relatively safe. We have learned to harden the target and patrol with vigilance.

And even in those suburbs and small towns where spree killings have occurred, the rates, per capita, are lower now than in previous decades. School is a safe place - until, as in Chardon, Ohio, the unspeakable happens. Then, even though the risks are low, it is fair to ask, why does this still happen? Why here, in America?

Let's be clear. There is no single, certain answer to these questions. The possible factors include failure by classmates, parents and school officials to see the warning signs; bullying and revenge; serious mental illness; violent role models; drugs; access to guns, and a culture that condones extremism.

America has its share of these factors, but which are significant and which are more prevalent here than across the Atlantic?

Warning signs

Students do not become mass killers overnight. They nurse their fantasies and they leak evidence. Insults, threats and plans are posted on websites. Classmates often know when a student is ready to strike back. Parents hear rumblings and have accurate gut sensations.

Within our country there are communities and neighborhoods and school districts that are relatively cohesive, vigilant and able to discuss warning signs of danger. There are some communities that are not as well integrated. They must be coached and helped.

After Columbine and Virginia Tech and other notorious school shootings, new programs to share information were developed and several plots were nipped in the bud. This evolution of information sharing occurs in other countries, but it is difficult to measure, nation to nation, who is ahead and who is behind. I see no proof that America is losing this race to improve detection of warning signs.

Bullying and revenge

We have too many bullies and too many youngsters at the mercy of bullies. But we also have a growing system of anti-bullying school programs. Despite rumors to the contrary, the Columbine killers were not bullied. There is no evidence that America, compared to other nations, has more bullies, more bullying, more victimization, and more victims who are ticking time bombs, hatching plots of lethal vengeance. However, we certainly can and should promote school programs that protect all children from stalking, hazing, and the new, evolving forms of abuse: Ostracism and humiliation through electronic social networks.

When boys are bullied they may fantasize about revenge. To dream of turning the tables on a bully is common to all eras, most cultures, and the source of drama, film and literature from the Elizabethan stage to the spaghetti Western. But whether a slowly evolving fantasy of mass murder is a product of mental illness, of bullying or of other sources, there are usually signs along the way.

Major mental illness

We do not have more major mental illness than most other countries. But we may be less caring of our mentally ill. Back in the Kennedy era, we launched community mental health programs to care for people with schizophrenia and similarly severe disorders, including depression. We wanted treatment available close to home, with compassionate supervision and with proper medication. We tried to stop the revolving door to the asylum, and, in fact, we tore down the large state hospitals. Our best intentions failed.

The program was never fully funded and our American system of care leaves much to be desired. The most serious mental illnesses, schizophrenia and depression, often become overt in adolescence. A boy who is smart enough to get into a good college becomes deluded, obsessed, strange, scary - and he gets rejected, isolated and stuck in a fantasy world. Those fantasies can become lethal. These forms of mental illness are seldom the source of homicide (far more often they torment and demoralize the disturbed individual). But when they are dangerous to others, we need good answers.

We do not have a sophisticated system of care and protection. If we did, Mr. Cho would not have killed 32 students at Virginia Tech. But America is really no worse than other nations when it comes to the numbers of seriously mentally ill, of violently mentally ill, of insufficiently treated violent mentally ill school-age boys. (Yes, we are talking about boys and young men; by far, they are the school shooters).

Violent role models

Violent role models, on the street, in the cinema, in the news, have been with us for as long as I recall, and are not limited to America. Back in the '60s, an American counter culture leader said, "Violence is as American as cherry pie." But other parts of the world, such as Northern Ireland, the Balkans, the children's armies of Africa, the terrorist camps of the Middle East, have their violent role models. Machismo is not an American word, nor is Hooligan.

Drugs

We do have drugs and a drug culture and aspects of this problem are more severe here than in many other parts of the world. Crime is connected to the drug trade and this crime can spill into the school. But the type of school shooting that occurs in the suburb is seldom connected to this urban issue. There may be an indirect connection, since drug wars arm young soldiers of drug wars, and arms are a large issue in America.

Access to guns

Access to guns is a significant factor in American school shootings. If kids could not and did not bring guns to school, we wouldn't have Columbine, Virginia Tech or Chardon, Ohio. There have been crimes with knives and bats and fists. But school shootings are gun crimes. Kids with guns kill kids at school.

I do not think America is an extremist nation, compared to other nations with bloody histories and despotic leaders. True, we have polarized political speech, and some of that speech is about access to guns. But the reason we have an American school shooting problem that exceeds other nations has to do with access to loaded weapons by kids who should not have that access.

I'm not offering a gun control solution. But any serious attempt to prevent school shooting will have to attack the problem by determining who should not be armed, and preventing dangerous boys from bringing guns to school.

The views expressed in this article are solely those of Frank Ochberg. For more on the subject of school shootings, Dr. Ochberg recommends reading reports by the U.S. Secret Service and the FBI.