School shootings since the 1700s which include just under 20 in the 1950s.
1700s 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 Indian entered the schoolhouse near present-day Greencastle, Pennsylvania, shot and killed schoolmaster Enoch Brown, and killed...
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Once you get to the 1966 University of Texas massacre, then you start seeing more and more mass shootings as the firepower one person could bring to bear increased.
From the late 1980s to the early 1990s the United States saw a sharp increase in gun and gun violence in the schools. According to a survey conducted by The Harvard School of Public Health "15% said that they had carried a handgun on their person in the past 30 days, and 4% said that they had taken a handgun to school in the past year." a sharp increase from just five years earlier. By 1993, the United States saw some of the most violent time is school shooting incidences.