Spaced Repetition
Spaced repetition is a practice technique that exploits the "forgetting curve" to maximize long-term memory retention. The core insight: the act of successfully retrieving fuzzy memory strengthens it far more than retrieving clear memory.
The "Wait-Lifting" Analogy
Justin Skycak describes spaced repetition as "wait-lifting":
- You are lifting information off the floor of long-term memory and raising it into working memory
- The fuzzier the memory, the heavier the lift
- Successfully completing a heavy lift = stronger memory (longer retention)
- Spacing creates the weight — wait long enough that the memory fades, then retrieve it
Just as in weightlifting:
- Too easy (memory too clear) = minimal strength gain; better to learn something new
- Too hard (memory too gone) = you can't retrieve it; nothing is strengthened
- Sweet spot = memory is fuzzy but retrievable with effort
Why Reviewing Should Feel Hard
Students often expect review to feel easy. But if review is easy, it means:
- Memory is still clear → the lift is trivial → almost no strengthening happens
- You'd be better off learning new material
An efficient teacher/system intentionally lets memory fade before the review session, so the retrieval exercise is effortful and productive.
Spaced Re-reading Doesn't Count
Re-reading brings information into working memory from the page, not from long-term memory. It bypasses the lift entirely. This is like having your spotter do the whole lift for you — no training effect.
The only time you should check reference material is when you've tried to recall and genuinely can't. Even then: look once for a cue, then close the reference and try to recall the rest without help.
Relation to Desirable Difficulties
Spaced repetition is one instance of a broader principle: introducing "desirable difficulties" into learning — making the task tough yet achievable. Other forms:
- Interleaving — mixing different types of problems rather than blocking by type
- Varied contexts — practicing the same skill in different settings
- Time pressure — reduces priming and forces harder retrieval
Connection to Deliberate Practice
Deliberate practice covers skill acquisition; spaced repetition covers retention. Both are necessary. You can acquire a skill perfectly and lose it if you don't review. You can review perfectly and never acquire if you don't practice new material.
Tools
Anki — a flashcard app with built-in spaced repetition algorithms. Both Oakley and many educators recommend it. The algorithm automatically schedules review at optimal intervals.
Sources
- advice-on-upskilling — Ch 9 (Learning), sections "Review Should Feel Challenging," "Learn Like You Lift," "Recall Before Re-reading"
- a-mind-for-numbers — Ch 10–11 (Memory), with practical techniques for index cards, memory palace integration, and spacing schedules