If you've noticed that the subways were strangely empty of school kids or that the streets were strangely full of them during school hours, you can stop contemplating that call to a truant officer. NYC public school students get today off because it's Brooklyn-Queens Day. The Queens Public Library explains:

Brooklyn-Queens Day originated as a Protestant holiday celebrated in the City of Brooklyn in 1829. Back then it was known, and fondly remembered by some, as Anniversary Day. Anniversary Day is celebrated annually on the first Thursday in June, commemorating the founding of the First Sunday School on Long Island. The first parade was held in Brooklyn June 1829.

The New York State Legislature enacted, in 1959 at the request of the Queens Federation of Churches, the bill permitting the schools in both Kings and Queens Counties to be closed on this day. It was signed by Governor Nelson A. Rockefeller.

However, this year, all students in all boroughs get the day off. Public school teachers, though, have a "development day."