Valerie Strauss:

Even though spasms of intense violence erupt on campuses occasionally and linger in the social consciousness, violence at schools across the country has been decreasing for a number of years.
That doesn’t necessarily mean schools are safe havens. Consider:
— Eighty-six percent of public schools in 2005-06 reported that one or more violent incidents, thefts of items valued at $10 or greater or other crimes had occurred — a rate of 46 crimes per 1,000 enrolled students.
— Almost a third of students ages 12 to 18 reported being bullied inside school.
— Nearly a quarter of teenagers reported the presence of gangs at their schools.

Indicators of School Crime and Safety.