In 1927, a madman killed 45 people at an elementary school in Bath Township, Michigan. Thirty-eight of the dead were children.
http://www.npr.org/templates/story/story.php?storyId=103186662
>> In 1927, a madman killed 45 people at an elementary school in Bath Township, Michigan <<
Yep, but it was a bombing, not a mass shooting — and that was back in the days when there were many, many fewer gun control laws in the USA.