C15 weakened
Explaining newly learned material to others (actually teaching it, not just preparing to) improves learners' own understanding on a delayed test more than studying it for themselves when learners studied the material expecting to teach it; a lasting gain is not established for a short explanation added after ordinary study.
Bounds: The learning of the person who explains, compared with studying for themselves; outcome delayed tests of the explained material; not the effect on the tutee (C5, C10) or peer discussion of concept questions (candidate K38). Evidence on file: Kobayashi 2018 (Japanese Psychological Research; meta-analysis of 28 studies; Hedges' g 0.35 for preparing to teach and 0.56 for teaching after preparing; benefits also after a delay; larger for interactive teaching); Fiorella & Mayer 2013 (Contemporary Educational Psychology; actually teaching after preparing helped on a delayed test about one week later). Expectancy and durability bound (added 2026-10-25, nightly attack): In three classroom experiments with 1,074 German grade 7–8 physics students, 15 minutes of explaining a lesson by voice message to a fictitious peer, with the materials at hand, beat 15 minutes of restudying on a test right afterwards but not on a test eight weeks later (difference not significant; a later advantage only for students with low or medium interest in physics) (Lachner et al. 2025). Lachner, Russ, Hübner, Sibley & Scheiter 2025 (Educational Psychology Review 37, 88; open access, CC BY; full text read on the publisher's site): preregistered one-stage individual-participant analysis of three analogous classroom experiments (project GRAIL) with 1,074 German grade 7–8 students in 11 schools; after the same 45-minute curriculum lesson on the converging lens, students were randomly assigned to 15 minutes of non-interactive teaching (recording a voice message to a fictitious peer, Mia, who had stated two common misconceptions; materials allowed, not to be read aloud) or 15 minutes of restudying the materials with notes. Because assignment came after the lesson, the teaching group had not studied expecting to teach. Scientific knowledge (15-item ROC-CI test, α = .72): immediate posttest β = 0.23, p < .001; delayed posttest eight weeks later β = 0.09, p = .110 (not significant); interest in physics moderated the delayed effect (β = −0.18, p = .043; low- and medium-interest students gained, high-interest students did not). Of the three sub-studies, Study 1 found no long-term effect and Study 3 (under review) no effect even immediately. The authors attribute the missing delayed effect to the short, single, open-book session and leave open whether repeated or closed-book teaching would last. Kill withheld: C15's kill-condition is about teaching after preparing to teach, and these students had not studied expecting to teach; the delayed estimate points the same way as the claim and was not shown to be zero (no equivalence test); one topic, one 15-minute dose. The evidence for a delayed benefit on file comes from studies in which learners studied expecting to teach (Fiorella & Mayer 2013; Kobayashi 2018). Consistent with this, Kobayashi 2024 (Educational Psychology Review 36, 26; meta-analysis of 39 studies; abstract only, paywalled) reports that teaching after studying with teaching expectancy beat studying without it, g = 0.48 [0.34, 0.63], while teaching after studying without teaching expectancy did not, g = −0.02 [−0.14, 0.11]; whether those outcomes were delayed is not stated in the abstract.
Attack record: 1 attack: 1 narrowed · Evidence links: 9 linked sources (3 supports, 4 limits, 2 challenges)