Teachers I have known.
Mr. A was my old Earth Science teacher in high school. He was damn good at his job; so good, he moved rapidly into administration at the school, then moved to administering another, more challenging school. He was as good an administrator as he was a teacher.
One time, following a lecture on tides and eclipses, Mr. A noticed me doodling on the whiteboard after class, trying to work out a model for what we had mentioned in class. He looked at my toy model, with a quarter-sized Earth, dime-sized moon, and grapefruit-sized sun, asked me what I was trying to do and nodded.
He removed my model with one swipe of the eraser, and took a marker, striding to the edge of the board. “Here you go. Here’s the moon.” He drew a dot on the edge of the board. “Here’s the Earth.” He added another dot. Then he strode purposefully to the other side of the board. “And here’s…” he said, drawing a vertical line tinged only with the faintest hint of a curve “…the friggin’ sun.”
I had, without realizing it, internalized the assumption that because the sun and the moon look about the same from our perspective on Earth that they are in any way comparable, and this attempt to put them in the same scale had been throwing me off but good. This wasn’t an exact demonstration of the relative scales of the objects of our solar system, but it made exactly the point I needed to be made, and Mr. A could identify the specific flaw in my thinking in need of correction and come up with a quick lesson to do so with about three second’s prep time and a whiteboard marker.
Like I said, damn good at his job.