This is the tragic story of the Bath School Massacre, the deadliest terror act on school property in US history. Over 100 children and adults were injured or killed on May 18, 1927 by an angry maniac who was upset about taxes. Yes, you saw that right... Taxes.
Sources
Bath School Disaster. Wikipedia.
K12 Academics. History of School Shootings.
“Maniac” by Harold Schechter
Putnam: Evil of Bath School Disaster remembered 89 years later. Judy Putnam. Lansing State Journal.