The full question read: "I heard that some American students may kill other people or shoot other students. Is that happens frequently? Why?"

Yes there are some American students who have killed other people and shot other students. While I wouldn't go as far as to say that this behavior is frequent, it has happened too often to realistically say that it is rare. According to the 1992–2009 School-Associated Violent Deaths Surveillance Study (SAVD)1, the number of school-associated homicides each year of the study ranged from 24 to 47. That averages out to almost one a week during the school year. Now to give you some perspective, there are about 70 million students in the U.S. (see source 2). So, even these non-rare occurrences are not a common problem.

The United States is not the only country where there have been school shootings (check out a Time Line of Worldwide School Shootings), but it does seem to be the country with the highest rate of such school violence.

U.S. News and World Report, claims that a Secret Service report shows that:

• Nearly all the shootings were committed by boys or young men.

• In over half of the incidents, fellow students were not the only targets, as attackers targeted administrators and other adults.

• In almost all the incidents, the attacker developed the idea to harm targets before actually doing so. In many cases, this planning was done weeks before the crimes were committed.3

It is this third point that may give us the biggest clue as to why school shootings happen more often in the U.S. than anywhere else in the world. The attackers generally plan their attack on the school in advance and this would include getting weapons. In the U.S. it is easier to get guns than in most other countries so this may be why the disgruntled youth in the U.S. are using guns. The U.S. also has a culture that glorifies guns in a way that most other Western countries do not. This may also lead attackers to choose to use guns.

There are many efforts underway in the U.S. to try and make schools safer places, including anti-bullying campaigns. The Centers for Disease Control and Prevention provides information about its own violence prevention programs on its website.

Sources:

1. National Center for Educational Statistics, “ Number of school-associated violent deaths of students, staff, and nonstudents, by type: School years 1992–93 to 2008–09 ”, (http://nces.ed.gov/programs/crimeindicators/ crimeindicators2010/tables/table_01_2.asp ), 27-Mar-2011.
   
   
2. Centers for Disease Control and Prevention. "Understanding School Violence - Facts Sheet." (http://www.cdc.gov/violenceprevention/pdf/ SchoolViolence_FactSheet-a.pdf), 27-Mar-2011.
   
   
3. Kingsbury, Alex. “After Columbine, School Shootings Proliferate”. U.S. News and World Report. (http://www.usnews.com/usnews/news/articles/ 070417/17shootings.htm), 27-Mar-2011.