That was the question my elementary school teacher asked the class a half-century ago.

“What day is this?”

I’m sure a dozen kids immediately answered, “Halloween!” Which may not have been as a big a deal then as it is now, but was big enough — and eagerly anticipated by children like the second- and third-graders in our class.

Our teacher was Mrs. Bolton. I remember her as impossibly old. She was, perhaps, 45. Maybe 50? When you are 7 or 8, it’s hard to tell, with these ancient fogies.

Actually, I’m sure we did not all shout “Halloween!” because as serious students in a serious class at a private school, none of us spoke without raising our hand and being called on. But I am certain a dozen hands shot up in the air. Back in a time when kids were competitive about showing off their knowledge.

Mrs. Bolton picked one out, and the child said, “Halloween!”

And then came the twist. “Yes,” she said, “but what else is today?”

Which threw us. What is it beyond Halloween?

Someone probably raised their hand, was called on and said, “October 31st!”

Mr. Bolton said, “Yes, but what else is today?”

By then, I figured it was some sort of riddle. I searched my mind. Someone, perhaps me, raised their hand and tentatively said, “Friday?” (Or whatever day Oct. 31 fell on, way back when.) The certainty was fading from us.

“Yes, but what else?”

And, eventually, the class fell silent. And Mrs. Bolton clearly was disappointed in us.

Today, she finally said, is Reformation Day.

Now, that normally would be a trick answer, and an obscure one, in most parts of the world.

But Mrs. Bolton taught second and third grade at First Lutheran School in Long Beach, California, and we all were students there and the parents of most of us were members of First Lutheran Church.

And she felt we ought to know that October 31 was/is Reformation Day.

Mrs. Bolton was a pill. (Years later, my mother would say, “Oh, yes, Mrs. Bolton … she hated little boys.” Which was like a light bulb going on in my head, years later, once my mother had said it. “Yeah! She did hate boys!”) But Mrs. Bolton was probably right about Reformation Day. Some 25, 30 kids at a Lutheran school, at least one of them ought to know.

“October 31 is Reformation Day.”

I have never forgotten that incident. And I remember every single year when October 31 rolls around. I even used it on my own children. “What day is today?” One of my daughters already has sent me a “Happy Reformation Day” e-mail.

Reformation Day, and the Reformation that followed it, are significant events, in Western history. It marked the beginning of a major break inside the Roman Catholic world,  the movement toward what would the Lutheran church, which them morphed into various strands of Protestantism. Reformation Day led to wars and revolutions and, depending on your historian, to concepts like the nation state and demands for freedoms of thought and worship …

On Reformation Day, Martin Luther is said to have nailed 95 theses — a list of observations, most of them more of a scholarly than politcal bent –  on the Castle Church door in the German city of Wittenberg. (I have been there; spectacularly underwhelming; the German government ought to spiff up the whole place and try to bring in tourists.)

Luther’s idea was that a big crowd would be at church the next day for All Saints Day (November 1), a significant Roman Catholic holiday back then, and the people in the congregation who could read Latin could read the theses. Luther was anticipating the crowd.

Within a few months, the theses had been printed (Gutenberg having recently invented the printing press) and spread throughout Europe.

The spark for the whole movement, and why it spread so quickly, was the worldliness of the Catholic Church of that time, which had generally been a far more political than religious institution for hundreds of years.

The specific event was the sale of “indulgences,” a practice intended to raise money for building St. Peter’s in Rome. The church authorized men to travel about and sell indulgences — which promised a shorter time in purgatory. (Think of them of a sort of “get out of purgatory” card.)

The faithful were buying their way into heaven, essentially, which struck Luther (and many others) as bad religion, even if it was a good money-raiser for the Vatican.

The whole hoo-hah got started on Reformation Day. Halloween (All Hallows Eve) on October 31, 1517.

And I will never forget the crabby Mrs. Bolton because of that. Well, and because she also made me sing alone in front of the class, which I hate-hate-hated and dreaded for about two weeks before it happened.

I remember her for that, and for “what day is this?”