Panati's _Every Origins..._ book supports the change in the calendar origin as well. His point being that the change in the Gregorian calendar by King Charles IX in France. As pointed out to some degree by others, France once celebrated New Year's beginning on March 25. This festival ran for a week with the exchange of gifts, and ended with parties on April 1.

IN 1564, King Charles IX decreed that with the adoption of the Gregorian calendar, New Year's be moved to January 1. Those who refused or forgot were ridiculed by being sent foolish gifts and invitations to nonexistent parties. The butt of such a prank was known as a "poisson d'avril." Panati further notes that Napoleon I also acquired "poisson d'avril" when he married Marie-Louise of Austria on 1 April 1810. Over a period of nearly two hundred years, the practice of playing such jokes spread from France to England to the US.

By coincidence, those with access to the Clarinet hierarchy may have noted that they carried an article concerning the history of this holiday on, April 1. In it, they cited the research of Steven Fanning, a professor in the history department of the University of Illinois at Chicago. In it, he was cited as saying that the playing of pranks of people who didn't keep up with the change in the calendar pretty much happened in most of Europe. He says that the origins behind the French term is unknown (though they were the first nation to adopt the Gregorian calendar).

One other cute point in that article was that April Fool's Day in Scotland is called "April Gawk" and the butt of a prank on that day is called a "gawk."