"That’s the main thing good tutors do differently. If motivation decreases, they switch to lighter content, or even transition into non-lesson conversation. If motivation increases, they ramp up the difficulty of the lesson."

I would say that's reasonable (but not optimal) if we're talking about an adult client who is footing the bill himself or herself. But in the case of, say, high school students, parents don't like that kind of laissez-faire ambiance.