In one sentence
German third graders made fewer spelling errors on words practised in an interleaved (mixed-rules) session than in a blocked session — both right after training and eight weeks later.
What the researchers did
Klimovich and Richter ran a preregistered classroom experiment with 147 German third graders. Children practised words governed by specific spelling rules (capitalisation; single vs multiple consonants; i vs ie; ss vs ß). Each child completed two training sessions: one in a blocked format and one interleaved, so every learner experienced both schedules.
The team also tested instructional guidance — prompts and explanations that highlight key features and push learners to compare rules — asking whether guidance boosts interleaving by supporting comparison. Outcomes covered practised words and transfer to new, unpractised words under the same rules, with an immediate post-test and an 8-week follow-up.
What they found
- Children made fewer spelling errors on words practised under the interleaved condition than under the blocked condition.
- The interleaved advantage appeared immediately after training and remained at the 8-week follow-up.
- Instructional guidance affected performance on new words sharing the same rules, but the pattern depended on prior knowledge.
- Guidance helped low prior-knowledge children during blocked practice on the immediate post-test.
- At follow-up, guidance benefited high prior-knowledge children during interleaved practice.
- Authors conclude interleaving supports lasting learning of spelling rules and transfer, especially for children who already know more.
What this means for learners and educators
- For spelling rules that look alike, prefer mixed practice sets over finishing one rule completely before the next — at least after a basic foothold.
- Expect interleaving to feel harder in the moment; this study’s delayed spelling accuracy favoured the mix.
- Add comparison prompts carefully: children with weaker baselines may need clearer scaffolding during blocked work first; stronger students may gain more from guidance inside interleaved sessions over time.
- Design transfer checks with new words under the same rules, not only the exact items drilled.
Limitations and what we don't know yet
The abstract does not report exact error rates or effect sizes here. Findings are for German orthography in third grade — other languages and ages may differ. Instructional guidance effects were moderated by prior knowledge, so a one-size prompt pack is unlikely. Whether a richer pre-teaching phase would help low prior-knowledge children harvest more from interleaving remains an open design question the authors flag for future work.