Did You Know That Today Is "Patriots' Day"?

The focus will likely be on the running of the Boston Marathon today, following last year's bombing. But did you know that the event is held on "Patriots' Day" every year?  I'd never heard of "Patriots' Day" until I lived in Boston myself for a couple of years, because it's not a national holiday. 

It commemorates the Battles of Lexington and Concord on April 19, 1775, the first battles of the American Revolution. The focus of the celebrations (beyond the marathon) is reenactments of those battles. (Below is home video from the 2010 reenactment, which for much of its 7 minutes makes the Battle of Lexington look like a junior high school dance, where the boys and girls stand separately and eye each other nervously and hesitantly from across the room.)

I can understand why it's a state holiday in Massachusetts.  But why, I wonder, is it also a public school holiday in Wisconsin?