Home · C15
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.
- Status
- weakened
- Last change
- 2026-10-25
- Serves
- Q1
- Ages
- grundskola-hog, gymnasium, vuxen-livslangt
- Area
- Learning from other people
- 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.
- What would kill this
- A large preregistered experiment or meta-analysis finds that teaching others after preparing gives no better delayed-test learning than studying alone for the same time. Promoted from K37 on 2026-10-16 in the broadening Jonatan approved 2026-10-16 (one new claim per uncovered area.
- Tutor consequence
- none yet
Attack record
1 attack: 1 narrowed
Reworded on 25 October 2026 (a change of wording, not an attack, so it is not counted). Shortened the claim sentence to the plain rule. The Lachner et al. 2025 study detail moved unchanged into limits; the Kobayashi 2024 detail was already there. No new numbers; status, survivals and kill-condition unchanged.
2026-10-25 narrowed
- Attack
- In a preregistered analysis of three randomised classroom experiments with 1,074 secondary-school students, explaining a just-taught physics lesson to a fictitious peer for 15 minutes beat restudying for the same time on an immediate test but not eight weeks later (β = 0.09, p = .110), so teaching others does not reliably improve the teacher's own understanding on a delayed test more than studying alone.
- Target
- claim-text
- Source
- Lachner, Russ, Hübner, Sibley & Scheiter 2025 | Educational Psychology Review 37, 88, DOI 10.1007/s10648-025-10060-0
- Steelmans to
- C15's sentence covers any actual explaining of newly learned material to others, with no condition on how learners studied or how long they taught; this is the largest test on file (about ten times the lab studies the claim rests on), in real classrooms, randomised, preregistered, with equal time on task and a long delay, and its delayed advantage was small and not significant, matching Kobayashi 2024's meta-analytic finding (abstract) that teaching after studying without teaching expectancy gives no benefit (g = −0.02).
- Why
- Nightly-attacks 2026-10-25 Europe/Stockholm, widened-search slot (C15, four consecutive fruitless searches). DOI checked on Crossref (title, five authors, Educational Psychology Review 37, article 88, published 2025-08-28) and Unpaywall (open access, CC BY, publisher version). Full text read on the publisher's article page (the PDF is behind a bot check from the box; not stored). Design: project GRAIL, three analogous experiments, German grade 7–8 physics, 11 schools; preregistered re-analysis (AsPredicted 26p4-7vsh); same 45-minute lesson on the converging lens (15-minute introduction plus 30 minutes of experiments) taught by one certified physics teacher; then random assignment to 15 minutes of non-interactive teaching (voice message to a fictitious peer responding to two misconceptions; materials allowed) or 15 minutes of restudying with notes. Scientific knowledge (ROC-CI test, 15 items, α = .72): immediate β = 0.23, p < .001; eight weeks later β = 0.09, p = .110; interest moderated the delayed effect (β = −0.18, p = .043). Sub-studies: Study 1 no long-term effect, Study 3 no effect immediately or delayed. Kill withheld: the teaching group had not studied expecting to teach, which C15's kill-condition requires; the delayed estimate is positive and not shown to be zero; one topic, one short open-book session (the authors' own explanation for the null). Not a restatement: the Bounds named no condition on teaching expectancy or dose, and open question 13 concerns written versus spoken teaching (here spoken). Not a duplicate (first ledger entry for C15). Peer reviewed; not a preprint. Status alive → weakened. Claim and Bounds rewritten same turn; brief, practical rule, limits and headline and the C15 front-page line rewritten.
- Rewrite
- claim-field+brief
Linked sources
9 linked sources (3 supports, 4 limits, 2 challenges)
Supports (3)
Limits (4)
Challenges (2)
Review state: first-pass draft, pending human review.