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 five-stage structure of every Lexy lesson:
- Stage 1 (Words): first exposure and an interactive quiz with pronunciation.
- Stage 2 (Lesson with Lexy): a live voice conversation, the first act of spaced retrieval.
- Stage 3 (Exercises): a varied check of the phrases five minutes after the dialogue.
- Stage 4 (Dialogue between two native voices): hearing the topic again from outside, in new phrasing.
- Stage 5 (Audio library and story): text to read and audio to relisten to at 2, 4 and 7 days, whenever you want.
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.
Try the method a meta-analysis backs up
Feel the effect of spaced spoken practice for yourself. The first two lessons of any of Lexy's 37 languages are free — from foundational English to practical Spanish for travel.