The Department of Justice put out a report in February that describes the statistics of violent death at school. One of the interesting findings is that between 1992 and 2010, the general trend has been slightly down. This despite an increased number of younglings and a supposed increase in the violence of culture.
2012, sadly, will bump the numbers up a bit.
The 1990’s were fairly flat, with around 30 kids killed at school per year. But then it dropped in half for the 1999-2000 year. My guess would be that this was a result of people paying attention after Columbine.
While most of these deaths are of course tragedies (I’m betting, though, that some were lil’ thugs getting greased by other lil’ thugs), the numbers are a lot smaller than what you might expect. According to THIS, in 2007 3,345 children (defined as age 0 to 19) died via homicide… with 21 being killed at school. That’s 0.63% of all murdered kids being murdered at school.
A bit of a problem arises when you define a 19-year-old as a “child,” though.