Teaching a class where the history is all wrong

Last night I dreamed I was standing at the board in my classroom, but the dates were off by a century — the Civil War in 1765, Rome falling in 1922 — and none of the kids blinked. They were taking notes, nodding, and I kept trying to erase it, but the chalk wouldn't come off the board. I woke up annoyed, which I think says more about me than the dream.