Spaced Repetition | Ed Tech Docs

Spaced Repetition: The Science of Never Forgetting

Spaced repetition is one of the most powerful, evidence-based learning techniques—capable of dramatically improving long-term retention with less total study time. Understanding and applying spacing effects can transform how you learn and remember information.

The Forgetting Curve

Ebbinghaus's Discovery (1885)

Key Finding: We forget exponentially without review

Forgetting Curve:

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100% ─┐
      │╲
 80%  │ ╲
      │  ╲___
 60%  │      ╲___
      │          ╲____
 40%  │               ╲_____
      │                     ╲______
 20%  │                            ╲______
      │
  0%  └────────────────────────────────────
      1h   1d    1w    1m    3m    6m

Without Review:

1 hour: Remember 60%
1 day: Remember 30%
1 week: Remember 10%
1 month: Remember ~2%

Combating Forgetting

Spaced Review:

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Review Schedule:
Day 1: Initial Learning (100%)
Day 2: First Review   (↑ 100%)
Day 4: Second Review  (↑ 100%)
Day 8: Third Review   (↑ 100%)
Day 16: Fourth Review (↑ 100%)
Month 1: (↑ 100%)
Month 3: (↑ 100%)

Result: Information moves from short-term to long-term memory

The Spacing Effect

What Is It?

Definition: Information studied over spaced intervals is remembered better than information studied in one session (massing), even with equal total study time.

Research:

Discovered by Ebbinghaus (1885)
Replicated in 1000+ studies
One of the most robust findings in psychology
Works across ages, subjects, and formats

Why It Works

1. Encoding Variability:

Different contexts at each review
Multiple retrieval paths created
Richer memory representations

2. Effortful Retrieval:

Slight forgetting between sessions
Retrieval effort strengthens memory
"Desirable difficulty"

3. Consolidation:

Sleep between sessions
Memory consolidation processes
Neural connections strengthened

4. Attention Freshness:

Novelty at each review
Reduced habituation
Better encoding

Optimal Spacing

General Principles

Expanding Intervals:

Start short, progressively lengthen

Example Schedule:

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Review 1: 1 day later
Review 2: 3 days later
Review 3: 1 week later
Review 4: 2 weeks later
Review 5: 1 month later
Review 6: 3 months later
Review 7: 6 months later

Factors Affecting Optimal Spacing

1. Material Difficulty:

Easy: Longer intervals
Hard: Shorter intervals

2. Retention Goal:

Short-term (exam): Closer spacing
Long-term (career): Wider spacing

3. Individual Performance:

Correct recall: Increase interval
Incorrect: Reset to shorter interval

4. Time Until Need:

Need in 1 week: Review every 2-3 days
Need in 1 year: Start with monthly reviews

The 10-Minute Rule

First Interval:

Review 10 minutes after initial learning for:

Error correction
Gap identification
Active recall practice
Immediate reinforcement

Spaced Repetition Systems (SRS)

How SRS Software Works

Algorithm (simplified):

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If correct:
  new_interval = current_interval × ease_factor
  
If incorrect:
  new_interval = 1 day
  ease_factor = ease_factor - 0.2

Adaptive Scheduling:

Tracks every card individually
Adjusts based on performance history
Optimises review scheduling
Prevents over/under-review

Leading SRS Platforms

Anki:

Most popular SRS
Highly customizable
20+ million flashcards shared
Mobile and desktop
Free (iOS paid)

Features:

SM-2 algorithm (Supermemo)
Image/audio support
Syncing across devices
Add-ons and plugins
Statistics and analytics

SuperMemo:

Original SRS (1985)
Most advanced algorithm
Incremental reading
Complex interface
Windows only

Algorithm Evolution:

SM-2 (1987): Simple, effective
SM-15 (2011): Optimal intervals
SM-17 (2016): Neural networks
SM-18 (2019): AI optimization

Quizlet:

500M+ users
Social features
Study modes variety
Teacher tools
Freemium model

RemNote:

Note-taking + SRS hybrid
Bidirectional links
Cloze deletions
PDF annotation
Knowledge graph

Effective Card Creation

Atomic Cards:

❌ Bad: "What are the features of React?"

✅ Good: "What does React's Virtual DOM optimise?"

One Concept Per Card:

❌ "What are props and state in React?"

✅ Card 1: "What are props in React?"

✅ Card 2: "What are state in React?"

Cloze Deletions:

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React components can be {{c1::functional}} or 
{{c2::class-based}}, with {{c1::functional}} 
components using {{c3::hooks}} for state management.

Image Occlusion:

Screenshot/diagram
Hide specific parts
Recall what's hidden
Perfect for anatomy, geography, diagrams

Common Pitfalls

1. Too Many New Cards:

Overwhelming review burden
Burnout
Start with 5-10/day

2. Passive Recognition:

Reading answer without retrieving
Not engaging memory
Use active recall

3. Context-Free Facts:

Isolated information
No connections
Link to existing knowledge

4. Suspended Cards:

Letting reviews pile up
Losing momentum
Do reviews daily

Application Strategies

Language Learning

Vocabulary Cards:

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Front: English word + example sentence
Back: Translation + audio pronunciation

Front: "The cat is *agile* and quick"
Back: 敏捷的 (mǐnjié de) [audio]

Grammar Patterns:

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Front: How to form past tense of regular verbs?
Back: Add -ed to base form
Example: walk → walked, play → played

Frequency-Based:

Start with most common words
1000 words = 75% of daily language
3000 words = 90% coverage

Technical Learning

Programming Concepts:

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Front: What does Array.map() return?
Back: A new array with transformed elements
Code: [1,2,3].map(x => x * 2) // [2,4,6]

API Methods:

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Front: How to make a GET request in fetch?
Back: fetch(url).then(res => res.json())

System Design:

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Front: What is the CAP theorem?
Back: In distributed systems, you can have only 
2 of 3: Consistency, Availability, Partition tolerance

Academic Subjects

Mathematics:

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Front: Pythagorean theorem formula?
Back: a² + b² = c²
Visual: [right triangle diagram]

Science:

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Front: What is photosynthesis?
Back: Plants convert CO₂ + H₂O + light → glucose + O₂
Equation: 6CO₂ + 6H₂O + light → C₆H₁₂O₆ + 6O₂

History:

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Front: When did World War II end?
Back: 1945 (VE Day: May 8, VJ Day: Sept 2)
Context: Allied victory, atomic bombs on Japan

Professional Development

Soft Skills:

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Front: STAR method for interviews stands for?
Back: 
- Situation
- Task
- Action
- Result

Business Concepts:

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Front: What is the Pareto Principle?
Back: 80% of effects come from 20% of causes
Examples: 80% revenue from 20% customers

Research-Backed Practices

Retrieval Practice

Active Recall:

Don't flip card immediately
Speak answer out loud
Write it down
Check accuracy

Benefits:

Strengthens memory trace
Identifies knowledge gaps
Metacognitive awareness
Better than re-reading

Interleaving

Spaced + Mixed Topics:

Don't:

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10 algebra problems
10 geometry problems
10 trigonometry problems

Do:

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Algebra, geometry, trig, algebra, trig, 
geometry, algebra, geometry, trig, algebra

Benefit: Forces discrimination between problem types

Pre-Testing

Study Before You Know:

Attempt cards before learning
Fail (expected)
Then study material
Review cards again

Why: Primes brain for information, improves encoding

Spacing Within Sessions

Don't: Review same card multiple times in one session

Do: Space even within session (20+ cards between repeats)

Optimizing Your System

Daily Routine

Consistency Over Volume:

15 minutes daily > 2 hours weekly
Morning reviews (best retention)
Review before forgetting
Never skip more than 2 days

Manageable Load:

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Start: 5 new cards/day
Week 1: 35 cards total
Week 2: +5 new = 40 reviews
Month 1: ~75 reviews/day
Month 6: ~150 reviews/day (steady state)

Maintenance Schedule

New Material: 5-20 cards/day

Review Time: 10-30 minutes/day

Long-Term: Sustainable forever

When to Graduate Cards

Criteria:

Correctly recalled 5+ times
Over 6+ month period
With increasing intervals
Consistently easy

Result: Move to "known" deck, occasional review only

Beyond Flashcards

Spaced Reading

Incremental Reading (SuperMemo):

Import article
Read sections over time
Create cards from highlights
Review spaced-ly

Spaced Writing

Technique:

Write summary after lecture
Rewrite from memory next day
Rewrite again 3 days later
Compare to original

Spaced Projects

Software Projects:

Return to old projects monthly
Refactor with new knowledge
Reinforces learning
Practical application

Limitations and Misconceptions

What Spacing Doesn't Do

Not Magic:

Still requires understanding
Can't replace initial learning
Won't fix poor encoding
Needs active engagement

Not for Everything:

Complex problem-solving
Creative thinking
Physical skills
Procedural knowledge

When NOT to Use SRS

Cramming for tomorrow's test
One-time information
Constantly changing info (news)
Information you use daily (already spaced naturally)

Measuring Success

Metrics

Retention Rate:

Target: 80-90%
Too high (>95%): Intervals too short
Too low (<70%): Intervals too long

Review Burden:

Manageable: 10-30 min/day
Overwhelming: >1 hour/day
Adjust new cards accordingly

Long-Term Growth:

Track known cards
Measure cumulative learning
Celebrate milestones

Combining with Other Techniques

Spaced + Elaboration

Each Review:

Explain in own words
Create analogies
Connect to prior knowledge
Add context

Spaced + Testing

Practice Tests:

Space practice exams
Review missed questions
Create cards for errors
Exponentially space retests

Spaced + Teaching

Feynman Technique:

Learn concept
Teach it (day later)
Identify gaps
Review & teach again (3 days)
Simplify explanation (1 week)

Getting Started

Week 1: Foundation

Day 1-2: Choose platform (Anki recommended)

Day 3-4: Create 10 cards from current learning

Day 5-7: Add 5 new cards daily, do reviews

Month 1: Building Habit

Daily reviews (no exceptions)
5-10 new cards/day
Focus on high-value information
Refine card quality

Long-Term: Mastery

Sustainable pace
Regular deck maintenance
Archive mastered content
Expand to new domains

Tools and Resources

Software

Anki: https://apps.ankiweb.net (Free, recommended)

AnkiWeb: Web version + syncing

AnkiDroid: Android app

AnkiMobile: iOS app ($25)

Alternatives:

RemNote
Quizlet
Memrise
Mnemosyne

Pre-Made Decks

Language: Frequency lists, grammar

Medical: AnKing, Zanki

Programming: CS fundamentals

Certification: AWS, PMP, etc.

Caution: Customise to your needs

Research Papers

Cepeda et al. (2006): Spacing effect meta-analysis
Karpicke & Roediger (2008): Retrieval practice
Dunlosky et al. (2013): Learning techniques effectiveness

Next Steps

Apply spaced repetition:

Complement Learning Methodologies
Enhance Microlearning effectiveness
Support English for Developers vocabulary
Reinforce Technical Writing principles

Spaced repetition transforms learning from cramming to long-term mastery. Start small, stay consistent, and trust the science—your future self will thank you.