Spaced Repetition for Kids: The Science Behind WordSprout

Have you ever noticed that your child can perfectly read a sight word on Tuesday but completely forget it by Friday? That's not a learning problem — it's a memory problem. And it has a well-researched solution: spaced repetition.

The Forgetting Curve

In 1885, psychologist Hermann Ebbinghaus discovered the forgetting curve: we forget new information at a predictable, exponential rate. Without review:

• After 20 minutes: We forget ~40%
• After 1 hour: We forget ~55%
• After 1 day: We forget ~65%
• After 1 week: We forget ~75%

But Ebbinghaus also discovered the fix: reviewing at strategically spaced intervals dramatically slows forgetting. Each successful review strengthens the memory, making the next forgetting curve shallower.

What Is Spaced Repetition?

Spaced repetition (SR) is a learning technique where review sessions are scheduled at increasing intervals:

1. Review new word → next review in 1 day
2. If correct → next review in 3 days
3. If correct again → next review in 7 days
4. If correct again → next review in 14 days
5. And so on...

If the word is forgotten at any point, the interval resets. This ensures your child reviews difficult words frequently and easy words occasionally — maximizing learning while minimizing time spent.

The SM-2 Algorithm

WordSprout uses the SM-2 algorithm — the most widely studied and validated spaced repetition algorithm. It was created by Piotr Woźniak in 1985 and is used by:

• Anki — the most popular flashcard app among medical students
• Duolingo — the world's most-used language learning app
• SuperMemo — the original spaced repetition software

How SM-2 Works (Simplified)

For each sight word, the algorithm tracks:

1. Ease Factor (how easy this word is for your child) — starts at 2.5
2. Interval (days until next review) — starts at 1
3. Status — new → learning → reviewing → mastered

When your child practices a word:

If correct:

• Ease factor increases slightly (word gets easier)
• Interval increases: next review = current interval × ease factor
• Word moves closer to "mastered" status

If incorrect:

• Interval resets to 1 day
• Ease factor decreases slightly (word needs more practice)
• Word stays in "learning" or returns to "reviewing"

Example Timeline for "said"

Day	Action	Result	Next Review
1	First seen	Learning	Day 2
2	Correct ✅	Learning	Day 4
4	Correct ✅	Reviewing	Day 10
10	Correct ✅	Reviewing	Day 28
28	Correct ✅	Mastered	Day 80
80	Correct ✅	Mastered	Day 228

In this example, the word "said" is mastered after 5 successful reviews over 28 days — with only 5 total exposures. Without spaced repetition, traditional methods might require 20+ exposures over the same period.

Why Spaced Repetition Is Perfect for Sight Words

1. Different Words, Different Paces

Some sight words (like "the" or "it") are learned in days. Others (like "through" or "thought") take weeks. SR naturally adapts — easy words get spaced out quickly, while hard words get frequent review.

2. Prevents "Illusion of Knowing"

Traditional flashcard drilling can create a false sense of mastery — your child seems to know the words today, but hasn't truly encoded them into long-term memory. SR's expanding intervals test long-term retention, not just short-term recognition.

3. Efficient Use of Time

Instead of reviewing all 220 Dolch words every day (which would take 30+ minutes), SR focuses each session on the words your child needs to review today — typically 10–15 words in a 5-minute session.

4. Reduces Frustration

Because SR doesn't over-review known words, children don't get bored. And because it doesn't under-review difficult words, they don't feel lost. The difficulty is always in the "just right" zone.

Spaced Repetition for Young Children: Our Adaptations

Standard SM-2 was designed for adult learners. WordSprout makes kid-friendly adjustments:

1. Shorter maximum intervals — We cap review intervals at ~6 months for PreK–K (vs. years for adults), because young children's vocabulary context is still developing.

2. Gentle resets — When a word is forgotten, we don't make the child feel like they're starting over. We show it as "Let's practice this one again!" rather than marking it as "incorrect."

3. Game-based review — SR review sessions are disguised as games. Children don't realize they're following a precise algorithm — they're just having fun matching, swatting, and building words.

4. Visual progress tracking — Children see their progress as word statuses (🌱 New → 🌿 Learning → 🌳 Reviewing → 🎯 Mastered), not as scores or grades.

The Research Behind It

• A 2016 meta-analysis of 254 studies found that spaced practice improved long-term retention by an average of 60% compared to massed practice (cramming).
• Duolingo's research team found that their SR-based approach helped users retain vocabulary 2.3× better than traditional methods.
• A 2020 study in the Journal of Educational Psychology specifically found that spaced repetition improved sight word acquisition in Kindergarten students compared to traditional flashcard drilling.

Try It Yourself

The best way to understand spaced repetition is to experience it. Try WordSprout's interactive flashcards with your child. After a few days of practice, you'll notice the algorithm adapting — words your child finds easy appear less often, while challenging words get extra attention.

Your child's progress is tracked automatically, and you can see exactly where they stand on the progress dashboard.