Spring 1988: Pinellas County, Florida. Pinellas Park High School -- two students in the cafeteria with guns fatally shoot an assistant principal and wound another teacher and a student teacher. (Later school officials would block distribution of a student newspaper containing the account of events.) Didn't even make the national news, maybe because there was only one death and it was an adult (though that casualties were so relatively light was pure luck). School violence is not new; it's only newly bloody enough to make the news.

Sources: http://journalism.arizona.edu/faculty/Patten/article.html and St. Petersburg Times article "Painful reminders for some" from the series "MASSACRE AT SCHOOL" by Stephen Hegarty, April 2, 1999.