Thursday is Brooklyn-Queens Day — and if you’re wondering why exactly your kids get to stay home from school, you’re not alone.

Allow us to explain.

The arcane holiday (also called Anniversary Day, Rally Day, Kids Day, and Welcome Back to Brooklyn Day) commemorates the creation of the first Sunday schools in Brooklyn and the founding of the Sunday School Union.

Brooklynites originally celebrated the day by removing their children from schools and parading down Bedford Avenue, and eventually, the next borough over followed suit with their own local traditions. The first Queens parade was held in 1829 according to the Queens Public Library.

Although most of today’s New Yorkers hardly know why the schools are closed, the holiday was once a hotbed of conflict. After Brooklyn was incorporated into New York City in 1898, the Board of Education refused to acknowledge the holiday. Brooklynites simply ignored their ruling and held their parade anyways, until the board gave in and recognized the holiday in 1902.

One letter to the editor from a 1902 edition of the Brooklyn Eagle reads, “Why must thousands of children stay from school and loaf all day simply because, perhaps one-tenth have a church calling them away?”

Tony Carnes, editor of A Journey through NYC Religions, said that “as the city changes, holidays like this take on new significance.”

When white ethnics moved away from Brooklyn in the ’50s and ’60s, Carnes said, the celebration was taken up by African-American protestants and was eventually recognized citywide.

The holiday remained an unofficial celebration until former Gov. Nelson D. Rockefeller officially established Brooklyn-Queens day in 1959.

But the holiday only gave the day off to schools in those two boroughs, and after years of bellyaching the United Federation of Teachers negotiated to bring the holiday to all five boroughs during their 2005 contract negotiations.

A Brooklyn-Queens Day celebration in 1944. Photo via the Library of Congress

Teachers spend the day at school for what’s called a “Development Day,” while most kids know Anniversary Day simply as an excuse to miss class for a day.

And although the parades are much smaller these days, there is one scheduled for tomorrow: 10 a.m. tomorrow starting Irving Square Park in Bushwick.