I was chatting with another tutor the other day, and he happened to mention his favorite metaphor (ok, technically a simile) for the results people get from tutoring.
Tutoring, he said, is like a magnifying glass. If someone can raise their score 20 points by studying seriously on their own, I can probably raise them 200 points. But if they put in nothing, that’s what they’ll get back. It doesn’t matter what you multiply zero by; it’s always still going to be zero.
I think that’s the most eloquently I’ve heard anyone put it.