I understand that many do not put much stock in Wiki data, however this comprehensive listing of all school violence since the 1700’s illustrates that this phenomenon is not new.
http://en.wikipedia.org/wiki/List_of_school_shootings_in_the_United_States
just one excerpt:
1760s[edit]
The earliest known United States shooting to happen on school property was the Pontiac’s Rebellion school massacre on July 26, 1764, where four Lenape American Indians entered the schoolhouse near present-day Greencastle, Pennsylvania, shot and killed schoolmaster Enoch Brown, and killed nine or ten children (reports vary). Only three children survived.[1]
The deadliest school attack was the Bath Michigan school bombing in the 1920s. The killer was Andrew Keyhoe and he was a school board member with full access.