Mix review of older material with study of new material in every session
Reserve part of every session for retrieving older material before it falls off the forgetting curve entirely.
Why it works
Without deliberate scheduling, older material is naturally crowded out by new content — a form of passive forgetting by displacement. Interleaving old and new material in every session forces each older item to remain active in the retrieval system, preventing the forgetting curve from running to completion. The retrieval of old material also provides schema hooks for the new material, making new encoding more efficient through integration with prior knowledge.
How to do it
- Begin each learning session with a 5-minute review of material from 3–7 days ago.
- After studying new material, end with a brief recall of the older items again.
- If you maintain a question bank, include questions from all previous sessions, not just the last one.
- Adjust the ratio of old-to-new based on upcoming deadlines and the age of the oldest reviewed material.
Evidence
Interleaving old and new material is supported by both the spacing effect literature and the contextual interference effect. It is standard practice in well-designed spaced repetition systems (Anki, Leitner box). Direct controlled trials for this specific "every-session" protocol are limited. (mechanistic)
The optimal ratio of old-to-new material in a session depends on the review load from prior material; an expanding archive of past material eventually consumes too much session time if not carefully managed.
Common mistake
Studying only new material and scheduling older material for separate "review sessions" that never happen, allowing the forgetting curve to run to completion between sessions.
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More practices for The Forgetting Curve: How Memory Decays and How to Fight It
- Review new material within 24 hours of learning it
The forgetting curve is steepest in the first day — a brief review before sleep captures material when it is most at risk.
- Space reviews at increasing intervals after each successful retrieval
After each successful review, increase the interval before the next one — this is how you make memories last for years on the same total time investment.
- Use what you forget as a diagnostic, not a verdict
Track which items are forgotten at each review interval — that pattern reveals the structure of your knowledge gaps more accurately than any self-assessment.
- Over-learn until retrieval is fluent, then stop
Continue practice just past the point of first correct retrieval — over-learning compresses the forgetting curve without requiring proportionally more time.
- Schedule learning before sleep to leverage overnight consolidation
New memories consolidate most effectively during sleep — learning shortly before sleep and reviewing shortly after waking exploits this biology.
Related concepts
- The Testing Effect: Why Retrieval Practice Beats Restudying
Retrieval practice, elaborative interrogation, and why the act of remembering makes memories stronger
- Active Recall: The Most Effective Way to Study
The testing effect, retrieval practice, and how to build active recall into every session
- Contextual Interference: Why Varied Practice Beats Blocked Repetition
Blocked vs. varied practice, the spacing effect, and why practice that feels harder builds skills that last