We’ve just plotted some data on school enrollment vs. year (and discussed the meaning of “enrollment” as a number).

Question: “What does the slope represent?”

Response: half-open mouths, half-shrugs, half-smiles, total silence. Their looks say: What are you talking about?

“Ok, try this: What does the slope tell you about the school?

Backs straighten (a bit). Eyes narrow in concentration. Conversation sputters once, twice, then takes off. I sit and listen. After some false starts, a few people put it together, and after another minute they’ve all got it.

They turn to me and now their looks say, Why would you ask us something so easy?