The Distributed Practice Effect on Classroom Learning: A Meta-Analytic Review of Applied Research
Mawson, W., & Kang, S. H. K. · 2025
grade Cmeta-analysisindependentunreplicatednumbers spot-checked
Sample
22 reports / 31 effect sizes / N>3,000
Population
K-12 and university classrooms; curriculum content.
Design
Classroom-ONLY spacing meta — the key lab-to-classroom translation source. Very high heterogeneity (I2=92%); retention intervals capped at 42 days.
Key findings
Real-classroom spacing effect d~0.54, well below lab estimates, with huge heterogeneity. Practical translation: fixed ~7-day gaps are most reliable, expanding intervals no better and sometimes negative, ~3 spaced exposures suffice ('less is more'), and effects can go NEGATIVE in primary grades.
Genetic confound
Low-moderate: mostly within-class/randomized; heterogeneity reflects design/population, not genetics.
Replication notes
Best estimate of the real-classroom spacing effect; below lab-inclusive estimates.
DOI / URL
10.3390/bs15060771
Effects
| Outcome | Metric | Value | Measure | Timing | Vs | Horizon | Class |
|---|---|---|---|---|---|---|---|
| Distributed vs massed in real classrooms (longest RI) | d | 0.54 [0.31,0.77] (vs lab-inclusive ~0.85) | mixed | delayed up to 42d; classroom | active-alternative | under-1yr | domain-skill |
| Schedule moderator | direction | fixed ~7-day gaps most consistent; EXPANDING intervals smaller/sometimes negative | mixed | delayed; classroom | active-alternative | under-1yr | domain-skill |
| Age/level moderator | direction | secondary > primary; PRIMARY grades produced the most NEGATIVE effects | mixed | delayed; classroom | active-alternative | under-1yr | domain-skill |
Cited by
- Spaced (distributed) practicestrong supportconf: highgc: low