A Randomized Controlled Trial of Interleaved Mathematics Practice
Rohrer, D., Dedrick, R. F., Hartwig, M. K., & Cheung, C.-N. · 2020
grade Arctindependentreplicatednumbers spot-checked
Sample
787 7th-graders, 54 classes, multiple schools
Population
7th-grade, multiple real public schools, authentic algebra curriculum, own untrained teachers.
Design
PREREGISTERED cluster-randomized trial. ~4-month practice, unannounced test ~1 month later. Test used a BLOCKED format (biased against interleaving). Meets WWC without reservations; replicates Rohrer 2015.
Key findings
Preregistered cluster RCT, large diverse sample, untrained teachers, delayed test, meets WWC without reservations, replicates Rohrer 2015: large effect (d=0.83), positive for all 15 teachers. Key caveats: the test is proximal researcher-designed (same problem kinds; standardized equivalent likely ~0.4), and the effect confounds discrimination + embedded SPACING + retrieval (the per-kind gradient tracks spacing dose).
Genetic confound
Domain-skill outcome; no g. Larger for novices.
Replication notes
Numbers verified. The strongest evidence in the interleaving literature; but the outcome is a proximal researcher-designed test (standardized equivalent likely ~0.4).
DOI / URL
10.1037/edu0000367
Effects
| Outcome | Metric | Value | Measure | Timing | Vs | Horizon | Class |
|---|---|---|---|---|---|---|---|
| Interleaved vs blocked, unannounced test ~1 month later | d | 0.83 [0.68,0.97]; 60.7% vs 37.6% | researcher-designed | delayed 1mo+; classroom | active-alternative | under-1yr | domain-skill |
| Consistency across 15 teachers | d range | all positive, 0.23 to 1.48 | researcher-designed | delayed 1mo+; classroom | active-alternative | under-1yr | domain-skill |
| Per-problem-kind (tracks spacing dose) | d | A 0.86 / B 0.63 / C 0.40 / D 0.34 | researcher-designed | delayed 1mo+; classroom | active-alternative | under-1yr | domain-skill |
Cited by
- Homework — effects by age and by dosagemixedconf: mediumgc: medium
- Interleaving (mixing problem types vs blocking)moderate supportconf: mediumgc: low