1977:

Stephen King publishes Rage under the nom de plume of Richard Bachman. In this intense short story, a student who is not among the popular kids, and who has a less-than-idyllic home life, brings his father's handgun to school and kills a teacher and (I believe) one other student. The year 1977 is remarkable for two reasons: first, none of the students who have participated in the sensationalistic copycat killings were alive in 1977; second, despite the fact that the book sold hundreds of thousands of copies, and the plot read like a HOWTO on school shootings, no school shootings were reported in 1977.