The two are not always compatible. My “lesson cost” principle is often evidence of it (?) but I was thinking about it again with regard to textbooks.

Too many textbooks are written like reference books rather than pedagogical tools. Granted, reference books can be highly effective for learning material. However that’s not the point of a textbook. Rather it is to guide the student through new and often tedious material so that s/he learns the material, and hopefully retains the knowledge.

Thus a text book should become less efficient on the whole in order to become more effective. Remind me again, in the margin perhaps, what “heteroskedasticity” is and why it’s a problem. Maybe do this for a few chapters after its first introduced. This carryover means I don’t have to flip back to the original chapter and refresh my memory.