Is It Worth Re-Explaining Someone Else's Course? The Research Debt Argument, Open Textbooks, Switching Textbooks, Minimal Manuals, and a Four-Way Split of Documentation
Compared with commercial textbooks, open textbooks showed no reliable difference in learning performance across 22 studies combined (g = 0.01), with fewer withdrawals but weaker evidence for that. Among four state-approved math textbooks in California, one scored about 0.05 standard deviations higher than the other three combined. Materials with a minimalist design (mostly rewritten manuals) had a large effect, but the studies are old, the samples small, and the meta-analysis did not go through journal review. The case that one-to-many explanation pays off and Diátaxis's four-way split are both arguments, not data; no study has directly tested re-explaining a course.