Most classic memory-psychology studies used simple numbers, shapes or nonsense syllables in the participant's own language. Does the spacing effect hold up as strongly for a living second language (L2), with its grammar, phonetics and idiom to absorb?
In 2022 the journal Language Learning published a thorough answer: a meta-analysis by Su Kyung Kim and Stuart Webb.
The scale of the study: 48 papers, 3,411 learners
The researchers gathered and standardised data from every experimental study of spaced second-language practice published over the preceding decades. The final sample included:
- 48 independent studies with control groups.
- 98 individual effect sizes.
- 3,411 participants of different ages learning second languages (English, Spanish, French, German and others).
The result: a weighted Hedges' g of 0.81 (p < .001). In social science statistics anything above 0.8 counts as a large effect. It means learners on a spaced schedule outperformed more than 79% of learners doing traditional massed practice.
"Spacing practice over time has a powerful, statistically robust and durable effect on second language acquisition. The effect stays exceptionally strong for both vocabulary and grammar." Kim & Webb, Language Learning (2022)
Key findings for language learners
Kim and Webb's analysis surfaced several details course designers usually miss:
- Delayed testing reveals the real gap: an immediate test right after the session shows little difference between groups. In delayed tests (after 7, 14, 30 days) the advantage of spacing grows geometrically.
- Audio and speech reinforcement: spaced repetition through listening and speaking held up better than visually rereading lists.
- Expanding intervals win: review after 1 day, then 3 days, then a week produces a more durable result than fixed, equal gaps.
How Kim & Webb (2022) shaped Lexy's audio library
This meta-analysis is the basis for the seven-stage structure of every Lexy lesson:
- Stage 1 (Words): first exposure and an interactive quiz with pronunciation.
- Stage 2 (Warm-up): a short written chat with Lexy: the same phrases in a new form before the voice lesson.
- Stage 3 (Lesson with Lexy): a live voice conversation, the first act of spaced retrieval.
- Stage 4 (Exercises): a varied check of the phrases five minutes after the dialogue.
- Stage 5 (Dialogue between two native voices): hearing the topic again from outside, in new phrasing.
- Stage 6 (Audio library and story): text to read and audio to relisten to at 2, 4 and 7 days, whenever you want.
- Stage 7 (Memory flashcards): spaced review of previous lesson phrases from lesson 2 onward for durable retention.
A "Send to Telegram" button also puts the lesson's audio straight into your messages, so you can replay the conversation in headphones on the way to work the next day.
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