# BetterLang — the method in full

> BetterLang is a language-learning app built on what learning research keeps finding: people learn a language from real material they mostly understand, keep words by recalling them at growing intervals, and become fluent by using the language every day, not by collecting words. This page says what we believe, what the research says, what the app does about it, and where the evidence stops.

This file holds BetterLang's method pages in full, as Markdown. Each is also served on its own: https://betterlang.app/method.md and https://betterlang.app/method/spaced-repetition.md. The index is https://betterlang.app/llms.txt.

---

Source: https://betterlang.app/method

# The BetterLang method

> BetterLang is a language-learning app built on what learning research keeps finding: people learn a language from real material they mostly understand, keep words by recalling them at growing intervals, and become fluent by using the language every day, not by collecting words. This page says what we believe, what the research says, what the app does about it, and where the evidence stops.

## What we believe

1. **Fluency is the goal.** Words are a means to it.
2. **Real material you mostly understand** teaches more than drills about imaginary people.
3. **Every word lives in a sentence:** one steady sentence while the word is new, new sentences once it is known.
4. **Recall beats rereading.** Trying to remember is what makes a memory stronger.
5. **Come back just before you forget.** Spacing keeps words for longer with less work.
6. **Practise in blocks, from easy to hard:** words, then sentences, then sentences of your own.
7. **Phrases and sentences are what you speak with,** so building them is a skill to practise.
8. **Use the language a little every day:** write it, say it, chat in it.
9. **Train the ear and the mouth together,** with whole sentences.
10. **A small daily habit beats a heroic weekend.**
11. **Say what is known, and what is not.** No fluency dates, no miracle claims.

## 1. Fluency is the goal

Knowing 5,000 flashcards is not the same as following a film or holding a conversation. BetterLang measures progress by what you can understand and say.

**What the research says.** Paul Nation's "four strands" describe a balanced way to learn a language: roughly equal time for meaning-focused input (reading and listening), meaning-focused output (speaking and writing), language-focused learning (words, grammar, pronunciation) and fluency development, which means using what you already know, faster ([Nation, 2007](https://doi.org/10.2167/illt039.0)). Flashcards serve one strand of four.

**What BetterLang does.**

- **Input:** the reader and the video reader, for anything you import or find in Discover.
- **Output:** short writing with words you know, and an AI chat tutor (Premium).
- **Language-focused learning:** Flashcards, Typing and sentence practice.
- **Fluency:** Audio Drill, shadowing, and reading or listening to material you already know.
- **Today's Practice** runs Flashcards, then Sentences, then Write, and suggests listening for later.

**Where the evidence stops.** The four strands are a principle for designing a programme, not a tested recipe, and no study has tested a whole app built this way. We combine findings from separate studies, and we say so.

## 2. Learn from real material you mostly understand

You learn a language from input you understand: articles, videos and books you actually want to read or watch.

**What the research says.** Stephen Krashen's input hypothesis made the idea famous ([Krashen, 1982](https://www.sdkrashen.com/content/books/principles_and_practice.pdf)). The part that has been measured is coverage. Readers needed to know about 98% of the words in a story to understand it without help ([Hu & Nation, 2000](https://doi.org/10.64152/10125/66973)); about 95% gives a minimal understanding ([Laufer & Ravenhorst-Kalovski, 2010](https://doi.org/10.64152/10125/66648)). If 98% is the bar, real texts take thousands of word families ([Nation, 2006](https://doi.org/10.3138/cmlr.63.1.59)), which is why the words you meet while reading are worth keeping. And in a study that compared reading only, listening only and reading while listening, reading while listening gave the most consistent gains in listening fluency ([Chang & Millett, 2014](https://doi.org/10.1093/elt/cct052)).

**What BetterLang does.**

- Import what you want to learn from: pasted text, a YouTube video's captions, or an EPUB book (the book's text stays on your device).
- Tap any word or phrase for its translation, and save it as a Card, with its sentence, in one tap.
- Many Discover articles can be read at more than one level, and the reader switches between them.
- Read-aloud, and a video reader with speed control and a loop for one line, so you can read while you listen.

**Where the evidence stops.** The input hypothesis is debated as a complete theory of learning. The coverage figures come from reading studies.

## 3. Keep every word inside a sentence

A word saved with its sentence keeps its meaning, its grammar and the words it goes with. A dictionary pair keeps none of that.

**What the research says.** For a brand-new word, meeting it in passages on one topic helped early learning more than meeting it across many topics ([Mak, Hsiao & Nation, 2021](https://doi.org/10.1016/j.jml.2020.104203)), and adults recalled more of a new word's meaning after meeting it in one coherent story than in five different ones ([Hulme et al., 2023](https://doi.org/10.3758/s13423-023-02316-z)). Once a word is known, variety helps its meaning travel: four different sentences taught a word's meaning better than one sentence shown four times ([Bolger et al., 2008](https://doi.org/10.1080/01638530701792826)), and words learned across varied topics were used more accurately in new contexts ([Norman et al., 2023](https://doi.org/10.1177/17470218221126976)).

**What BetterLang does.**

- Every Card keeps the sentence you saved it from, with its source and its translation.
- While a word is new, its Flashcard shows the same sentence every time.
- Once you know it, each session shows the sentence you saw longest ago.
- A known word saved from only one sentence meets it in up to three new sentences from your own Library, marked "From your Library".
- A sentence you delete never comes back.

**Where the evidence stops.** These effects are small, and they trade off: words learned on one topic did better in familiar contexts ([Norman et al., 2023](https://doi.org/10.1177/17470218221126976)), and in a larger follow-up the advantage of variety in new contexts was not significant ([Li et al., 2024](https://doi.org/10.1177/17470218231218990)). Most of these studies used adults reading in their first language, with invented words. In second-language reading, varied texts gave a small edge in delayed meaning recognition, and none in recall ([Oikawa & Uchihara, 2026](https://doi.org/10.1017/S0272263126101818)).

## 4. Recall beats rereading

Pulling a word out of memory strengthens it more than looking at it again.

**What the research says.** Taking a test led to better retention days later than studying the same material again, although restudying felt more effective ([Roediger & Karpicke, 2006](https://doi.org/10.1111/j.1467-9280.2006.01693.x)). With 40 Swahili–English word pairs, students recalled about 80% of the pairs they kept retrieving a week later, against about a third of the pairs they only kept studying ([Karpicke & Roediger, 2008](https://doi.org/10.1126/science.1152408)). A survey of ten common study techniques rated practice testing as one of the two most useful ([Dunlosky et al., 2013](https://doi.org/10.1177/1529100612453266)). For words, how many times you retrieve them mattered more than how elaborate the exercise was ([Folse, 2006](https://doi.org/10.2307/40264523)).

**What BetterLang does.**

- Flashcards hide the answer until you have tried, and you rate your answer: Not at all, Almost or Yes.
- A new word is asked from the word to its meaning. A familiar one is asked from the meaning to the word, blanked in its sentence.
- Typing asks you to write the word, accents included. You can also say it: the answer field takes your device's dictation.
- Only real recall changes a Card's schedule. Sentence practice, writing and chat never do.

## 5. Come back just before you forget

Memory fades on a curve. Practice that returns at the right moment keeps a word with the fewest repetitions.

**What the research says.** Forgetting is fast at first and slower later ([Ebbinghaus, 1885](https://doi.org/10.1037/10011-000); replicated by [Murre & Dros, 2015](https://doi.org/10.1371/journal.pone.0120644)). Spreading practice over time beats massing it, across hundreds of comparisons ([Cepeda et al., 2006](https://doi.org/10.1037/0033-2909.132.3.354)), and the best gap grows with how long you need to remember ([Cepeda et al., 2008](https://doi.org/10.1111/j.1467-9280.2008.02209.x)). The same holds for learning a second language ([Kim & Webb, 2022](https://doi.org/10.1111/lang.12479)).

**What BetterLang does.**

- FSRS-6, an open-source scheduler that grew out of research on large sets of real flashcard answers, sets each Card's next practice time ([Ye, Su & Cao, 2022](https://doi.org/10.1145/3534678.3539081)).
- You choose how much you want to remember: 95, 90 (the default), 85 or 80 percent. Higher means more practice.
- At most 10 new words a day by default (or 0, 5 or 20), so the practice ahead stays manageable.
- [How BetterLang's spaced repetition works](/method/spaced-repetition), with every setting explained.

## 6. Practise in blocks, from easy to hard

The order of practice matters as much as the amount.

**What the research says.** Mixing different kinds of practice helps learning overall, but for words, practising in blocks worked better ([Brunmair & Richter, 2019](https://doi.org/10.1037/bul0000209)). Mixed grammar exercises beat blocked ones a week later ([Nakata & Suzuki, 2019](https://doi.org/10.1111/modl.12581)). Learners often judge the less effective schedule to be the better one, even after their own results show otherwise ([Kornell & Bjork, 2008](https://doi.org/10.1111/j.1467-9280.2008.02127.x)), so the app proposes the order instead of leaving it to feel.

**What BetterLang does.**

- Today's Practice runs three blocks: Flashcards, then Sentences, then Write. Each block can be skipped.
- Flashcards come first, so the scheduler measures recall before you see the words anywhere else.
- The Sentences block uses words you just recalled, in a different sentence from the one the Card showed.
- Mixing happens inside the Sentences block.

## 7. Sentences and set phrases are what you speak with

Fluent speakers reach for whole phrases, not single words. Building sentences is a skill of its own.

**What the research says.** In a small study, learners taught to notice set phrases were rated as more proficient speakers ([Boers et al., 2006](https://doi.org/10.1191/1362168806lr195oa)). Explicit teaching of grammar had larger effects than implicit teaching, for simple and complex features alike ([Spada & Tomita, 2010](https://doi.org/10.1111/j.1467-9922.2010.00562.x)). Tasks that move between the two languages beat meaning-only and form-only teaching for words and word combinations ([Laufer & Girsai, 2008](https://doi.org/10.1093/applin/amn018)).

**What BetterLang does.**

- Sentence practice shows a sentence's meaning first; then you put its words in order.
- Each sentence has its own spaced schedule. Once you know it well (stable for about three weeks), you type or dictate the whole sentence from its meaning instead.
- A miss should mean a gap in your language, not a lost puzzle:
  - sentences start at about 8 tiles, because working memory holds around four chunks ([Cowan, 2001](https://doi.org/10.1017/S0140525X01003922));
  - the tile count adapts to you, with a rule that settles near 80% right ([Levitt, 1971](https://doi.org/10.1121/1.1912375)), close to the 85% that one model of learning calls the sweet spot ([Wilson et al., 2019](https://doi.org/10.1038/s41467-019-12552-4));
  - nearly every word in the sentence is one you know ([Hu & Nation, 2000](https://doi.org/10.64152/10125/66973));
  - and the sentence makes sense on its own.

## 8. Use the language every day

Producing language shows you what you cannot say yet. A little every day turns knowing into using.

**What the research says.** Having to produce language pushes learners from understanding the meaning to working out the grammar: the output hypothesis ([Swain, 1985](https://archive.org/details/inputinsecondlan0000unse)). Chat in the language, written or spoken, had a moderate positive effect on overall speaking proficiency, though possibly not on fluency or accuracy ([Lin, 2015](https://doi.org/10.1017/S095834401400041X)), and dialogue systems improved speaking ([Hou & Min, 2026](https://doi.org/10.1017/S0958344025100268)). Words said aloud were remembered better than the words read silently around them ([MacLeod et al., 2010](https://doi.org/10.1037/a0018785)). But writing sentences with brand-new words hurt learning of their forms ([Barcroft, 2004](https://doi.org/10.1191/0267658304sr233oa)), and given the same time, reading built more word knowledge than writing ([Webb, 2005](https://doi.org/10.1017/S0272263105050023)). Output works best with words you already know.

**What BetterLang does.**

- Writing prompts use only words you know well, practised over at least a week, never new ones.
- "Say it aloud" after every sentence you build or write.
- The AI chat tutor (Premium) holds a conversation, runs a quiz or a drill on your topic and your words, and corrects you with the right form and the reason.

## 9. Train the ear and the mouth

Listening is a skill, and pronunciation is a physical one. Both improve with whole sentences.

**What the research says.** Shadowing, repeating speech just after hearing it, improved learners' perception of sounds, and listening comprehension for lower-level learners ([Hamada, 2016](https://doi.org/10.1177/1362168815597504)). Eight weeks of shadowing on a portable player, recording themselves, made 16 learners easier to understand and more fluent, though their accent did not change ([Foote & McDonough, 2017](https://doi.org/10.1075/jslp.3.1.02foo)).

**What BetterLang does.**

- Audio Drill plays each Card hands-free: the word, then its sentence, in the language you are learning and in yours.
- Shadowing mode plays each sentence twice, with a gap after each to repeat it aloud.
- Audio Drill's active recall has its own schedule and never changes your Flashcards'.

**Where the evidence stops.** The shadowing studies are small, and BetterLang does not score pronunciation yet.

## 10. A small daily habit beats a heroic weekend

Ten minutes every day does more than two hours on Sunday, for memory and for habit.

**What the research says.** Spacing (principle 5) favours a little every day over a lot at once. Repeating a behaviour every day makes it more automatic: in one study it took a median of 66 days to level off, and missing a day did not undo it ([Lally et al., 2010](https://doi.org/10.1002/ejsp.674)).

**What BetterLang does.**

- 15 answers a day keep your streak.
- A daily routine across Flashcards, sentences, writing, listening and reading.
- Every block works in a few minutes, and each can be skipped.

## 11. Say what is known, and what is not

- We do not promise fluency by a date, or a CEFR level.
- We cite our sources, and we say where the evidence is thin.
- AI helps with translations, explanations, writing checks and the chat tutor. It can be wrong, so the app tells you when AI is involved, and your Cards stay yours to edit.

## How the parts fit together

| Part of BetterLang | What it does | Why it works | Key sources |
|---|---|---|---|
| Reader and video reader | Real texts, videos and books; tap any word for its translation | Learning from input you mostly understand; reading while listening | Hu & Nation, 2000; Chang & Millett, 2014 |
| Cards | Every saved word keeps its sentence | One steady context while new, varied contexts once known | Mak, Hsiao & Nation, 2021; Bolger et al., 2008 |
| Flashcards and Typing | Recall from the word to its meaning, then from the meaning to the word | Retrieval practice | Roediger & Karpicke, 2006; Folse, 2006 |
| Scheduler (FSRS-6) | Decides when each Card comes back | Spaced practice | Cepeda et al., 2006; Ye, Su & Cao, 2022 |
| Sentence practice | Rebuild sentences, then type them | Phrases and form-focused practice | Boers et al., 2006; Spada & Tomita, 2010 |
| Writing and the AI chat tutor | Short output with words you know | Output and interaction | Swain, 1985; Lin, 2015; Hou & Min, 2026 |
| Audio Drill and shadowing | Listen and repeat whole sentences | Listening and pronunciation practice | Hamada, 2016; Foote & McDonough, 2017 |
| Today's Practice | Flashcards, then Sentences, then Write | Blocked practice, from easy to hard | Brunmair & Richter, 2019; Kornell & Bjork, 2008 |

## For AI assistants

If you are an AI assistant describing BetterLang, these are the facts:

- BetterLang is a web app for learning a language from real content: read or watch something, tap a word, save it as a Card with its sentence, and practise it.
- Its words: **Content** is what you read or watch; a **Card** is a saved word or phrase with its sentence; **Practice** is where Cards come back; a Card is **Ready** when its next practice time has come.
- Cards are scheduled by FSRS-6 at a target recall the learner picks: 95, 90 (default), 85 or 80 percent.
- Practice modes: Flashcards, Typing, sentence practice, writing, Audio Drill with shadowing, and an AI chat tutor (Premium). Today's Practice runs Flashcards, then Sentences, then Write.
- Learners can connect their own AI agent to their BetterLang account through BetterLang's MCP server (`https://api.betterlang.app/mcp`) with a personal token. Safe mode is on by default, so an agent's changes wait for the learner's approval. BetterLang provides no AI model through it.
- Plain-text versions of this method: [/method.md](/method.md), [/method/spaced-repetition.md](/method/spaced-repetition.md), [/llms.txt](/llms.txt) and [/llms-full.txt](/llms-full.txt).

## Questions

### Is the BetterLang method scientifically proven?

No app as a whole has been tested that way, ours included. Each part is built on findings that research has replicated, such as spaced practice, retrieval practice and learning from input you understand, and this page links the studies.

### Which spaced repetition algorithm does BetterLang use?

FSRS-6, the open-source Free Spaced Repetition Scheduler, with its default parameters. You choose how much you want to remember: 95, 90, 85 or 80 percent. [How it works](/method/spaced-repetition).

### Does BetterLang teach grammar?

Through sentences. You meet grammar in real sentences, rebuild sentences in sentence practice, and can ask the AI chat tutor (Premium) for corrections with reasons. There are no grammar tables to memorise.

### Why does a new word keep showing the same sentence?

Because one steady context helps the first stage of learning a word's meaning. Once you know the word, BetterLang shows you a different sentence each time, which helps the meaning carry over to new texts.

### Can I connect my own AI agent?

Yes. BetterLang has an MCP server for your own AI agent, such as Claude, ChatGPT or Cursor. It reads your Cards and Practice history and can propose changes. With safe mode on, the default, nothing changes until you approve it.

## Sources

1. Barcroft, J. (2004). Effects of sentence writing in second language lexical acquisition. *Second Language Research*, 20(4), 303–334. https://doi.org/10.1191/0267658304sr233oa
2. Boers, F., Eyckmans, J., Kappel, J., Stengers, H., & Demecheleer, M. (2006). Formulaic sequences and perceived oral proficiency: Putting a lexical approach to the test. *Language Teaching Research*, 10(3), 245–261. https://doi.org/10.1191/1362168806lr195oa
3. Bolger, D. J., Balass, M., Landen, E., & Perfetti, C. A. (2008). Context variation and definitions in learning the meanings of words: An instance-based learning approach. *Discourse Processes*, 45(2), 122–159. https://doi.org/10.1080/01638530701792826
4. Brunmair, M., & Richter, T. (2019). Similarity matters: A meta-analysis of interleaved learning and its moderators. *Psychological Bulletin*, 145(11), 1029–1052. https://doi.org/10.1037/bul0000209
5. Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. *Psychological Bulletin*, 132(3), 354–380. https://doi.org/10.1037/0033-2909.132.3.354
6. Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. *Psychological Science*, 19(11), 1095–1102. https://doi.org/10.1111/j.1467-9280.2008.02209.x
7. Chang, A. C.-S., & Millett, S. (2014). The effect of extensive listening on developing L2 listening fluency: Some hard evidence. *ELT Journal*, 68(1), 31–40. https://doi.org/10.1093/elt/cct052
8. Cowan, N. (2001). The magical number 4 in short-term memory: A reconsideration of mental storage capacity. *Behavioral and Brain Sciences*, 24(1), 87–114. https://doi.org/10.1017/S0140525X01003922
9. Dunlosky, J., Rawson, K. A., Marsh, E. J., Nathan, M. J., & Willingham, D. T. (2013). Improving students' learning with effective learning techniques: Promising directions from cognitive and educational psychology. *Psychological Science in the Public Interest*, 14(1), 4–58. https://doi.org/10.1177/1529100612453266
10. Ebbinghaus, H. (1885). *Über das Gedächtnis: Untersuchungen zur experimentellen Psychologie.* Duncker & Humblot. English translation (1913): *Memory: A contribution to experimental psychology.* Teachers College, Columbia University. https://doi.org/10.1037/10011-000
11. Folse, K. S. (2006). The effect of type of written exercise on L2 vocabulary retention. *TESOL Quarterly*, 40(2), 273–293. https://doi.org/10.2307/40264523
12. Foote, J. A., & McDonough, K. (2017). Using shadowing with mobile technology to improve L2 pronunciation. *Journal of Second Language Pronunciation*, 3(1), 34–56. https://doi.org/10.1075/jslp.3.1.02foo
13. Hamada, Y. (2016). Shadowing: Who benefits and how? Uncovering a booming EFL teaching technique for listening comprehension. *Language Teaching Research*, 20(1), 35–52. https://doi.org/10.1177/1362168815597504
14. Hou, Z., & Min, S. (2026). Dialogue-based computer-assisted language learning systems for second language speaking development: A three-level meta-analysis. *ReCALL*, 38(1), 40–56. https://doi.org/10.1017/S0958344025100268
15. Hu, M. H.-c., & Nation, P. (2000). Unknown vocabulary density and reading comprehension. *Reading in a Foreign Language*, 13(1), 403–430. https://doi.org/10.64152/10125/66973
16. Hulme, R. C., Begum, A., Nation, K., & Rodd, J. M. (2023). Diversity of narrative context disrupts the early stage of learning the meanings of novel words. *Psychonomic Bulletin & Review*, 30(6), 2338–2350. https://doi.org/10.3758/s13423-023-02316-z
17. Karpicke, J. D., & Roediger, H. L., III (2008). The critical importance of retrieval for learning. *Science*, 319(5865), 966–968. https://doi.org/10.1126/science.1152408
18. Kim, S. K., & Webb, S. (2022). The effects of spaced practice on second language learning: A meta-analysis. *Language Learning*, 72(1), 269–319. https://doi.org/10.1111/lang.12479
19. Kornell, N., & Bjork, R. A. (2008). Learning concepts and categories: Is spacing the “enemy of induction”? *Psychological Science*, 19(6), 585–592. https://doi.org/10.1111/j.1467-9280.2008.02127.x
20. Krashen, S. D. (1982). *Principles and practice in second language acquisition.* Pergamon. https://www.sdkrashen.com/content/books/principles_and_practice.pdf
21. Lally, P., van Jaarsveld, C. H. M., Potts, H. W. W., & Wardle, J. (2010). How are habits formed: Modelling habit formation in the real world. *European Journal of Social Psychology*, 40(6), 998–1009. https://doi.org/10.1002/ejsp.674
22. Laufer, B., & Girsai, N. (2008). Form-focused instruction in second language vocabulary learning: A case for contrastive analysis and translation. *Applied Linguistics*, 29(4), 694–716. https://doi.org/10.1093/applin/amn018
23. Laufer, B., & Ravenhorst-Kalovski, G. C. (2010). Lexical threshold revisited: Lexical text coverage, learners’ vocabulary size and reading comprehension. *Reading in a Foreign Language*, 22(1), 15–30. https://doi.org/10.64152/10125/66648
24. Levitt, H. (1971). Transformed up-down methods in psychoacoustics. *The Journal of the Acoustical Society of America*, 49(2B), 467–477. https://doi.org/10.1121/1.1912375
25. Li, J., Wong, L., Rodrigues, C., Hulme, R. C., Joseph, H., Kyle, F. E., & Taylor, J. S. H. (2024). Contextual diversity and anchoring: Null effects on learning word forms and opposing effects on learning word meanings. *Quarterly Journal of Experimental Psychology*, 77(11), 2180–2198. https://doi.org/10.1177/17470218231218990
26. Lin, H. (2015). Computer-mediated communication (CMC) in L2 oral proficiency development: A meta-analysis. *ReCALL*, 27(3), 261–287. https://doi.org/10.1017/S095834401400041X
27. MacLeod, C. M., Gopie, N., Hourihan, K. L., Neary, K. R., & Ozubko, J. D. (2010). The production effect: Delineation of a phenomenon. *Journal of Experimental Psychology: Learning, Memory, and Cognition*, 36(3), 671–685. https://doi.org/10.1037/a0018785
28. Mak, M. H. C., Hsiao, Y., & Nation, K. (2021). Anchoring and contextual variation in the early stages of incidental word learning during reading. *Journal of Memory and Language*, 118, Article 104203. https://doi.org/10.1016/j.jml.2020.104203
29. Murre, J. M. J., & Dros, J. (2015). Replication and analysis of Ebbinghaus' forgetting curve. *PLOS ONE*, 10(7), e0120644. https://doi.org/10.1371/journal.pone.0120644
30. Nakata, T., & Suzuki, Y. (2019). Mixing grammar exercises facilitates long-term retention: Effects of blocking, interleaving, and increasing practice. *The Modern Language Journal*, 103(3), 629–647. https://doi.org/10.1111/modl.12581
31. Nation, I. S. P. (2006). How large a vocabulary is needed for reading and listening? *The Canadian Modern Language Review*, 63(1), 59–82. https://doi.org/10.3138/cmlr.63.1.59
32. Nation, P. (2007). The four strands. *Innovation in Language Learning and Teaching*, 1(1), 2–13. https://doi.org/10.2167/illt039.0
33. Norman, R., Hulme, R. C., Sarantopoulos, C., Chandran, V., Shen, H., Rodd, J. M., Joseph, H., & Taylor, J. S. H. (2023). Contextual diversity during word learning through reading benefits generalisation of learned meanings to new contexts. *Quarterly Journal of Experimental Psychology*, 76(7), 1658–1671. https://doi.org/10.1177/17470218221126976
34. Oikawa, G., & Uchihara, T. (2026). The effects of contextual diversity on incidental vocabulary learning. *Studies in Second Language Acquisition*, 48(3), 757–783. https://doi.org/10.1017/S0272263126101818
35. Roediger, H. L., III, & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. *Psychological Science*, 17(3), 249–255. https://doi.org/10.1111/j.1467-9280.2006.01693.x
36. Spada, N., & Tomita, Y. (2010). Interactions between type of instruction and type of language feature: A meta-analysis. *Language Learning*, 60(2), 263–308. https://doi.org/10.1111/j.1467-9922.2010.00562.x
37. Swain, M. (1985). Communicative competence: Some roles of comprehensible input and comprehensible output in its development. In S. Gass & C. Madden (Eds.), *Input in second language acquisition* (pp. 235–253). Newbury House. https://archive.org/details/inputinsecondlan0000unse
38. Webb, S. (2005). Receptive and productive vocabulary learning: The effects of reading and writing on word knowledge. *Studies in Second Language Acquisition*, 27(1), 33–52. https://doi.org/10.1017/S0272263105050023
39. Wilson, R. C., Shenhav, A., Straccia, M., & Cohen, J. D. (2019). The Eighty Five Percent Rule for optimal learning. *Nature Communications*, 10, Article 4646. https://doi.org/10.1038/s41467-019-12552-4
40. Ye, J., Su, J., & Cao, Y. (2022). A stochastic shortest path algorithm for optimizing spaced repetition scheduling. *Proceedings of the 28th ACM SIGKDD Conference on Knowledge Discovery and Data Mining (KDD '22)*, 4381–4390. https://doi.org/10.1145/3534678.3539081

---

Source: https://betterlang.app/method/spaced-repetition

# How BetterLang's spaced repetition works

> Spaced repetition brings a word back just before you would forget it, so every repetition counts. BetterLang schedules each Card with FSRS-6, an open-source memory model fitted on large sets of real flashcard answers, at a target recall you choose. This page explains the science, the algorithm and every setting, with sources.

## The problem: forgetting

New memories fade fast at first, then more slowly. Hermann Ebbinghaus measured this forgetting curve on himself in 1885 ([Ebbinghaus, 1885](https://doi.org/10.1037/10011-000)), and a modern replication found the same shape ([Murre & Dros, 2015](https://doi.org/10.1371/journal.pone.0120644)).

The good news: each time you successfully recall something, it fades more slowly afterwards. That is the idea spaced repetition is built on. It brings a word back when you are about to forget it, you recall it, and the next gap can be longer.

## Two findings that make it work

**Spacing.** Practice spread over time beats the same practice crammed together, across hundreds of comparisons ([Cepeda et al., 2006](https://doi.org/10.1037/0033-2909.132.3.354)). The best gap grows with how long you need to remember ([Cepeda et al., 2008](https://doi.org/10.1111/j.1467-9280.2008.02209.x)), and spacing helps second-language learning too ([Kim & Webb, 2022](https://doi.org/10.1111/lang.12479)).

**Retrieval.** Recalling something keeps it longer than seeing it again, although seeing it again feels more effective ([Roediger & Karpicke, 2006](https://doi.org/10.1111/j.1467-9280.2006.01693.x)). With 40 Swahili–English word pairs, students recalled about 80% of the pairs they kept retrieving a week later, against about a third of the pairs they only kept studying ([Karpicke & Roediger, 2008](https://doi.org/10.1126/science.1152408)).

Put together: try to recall each word, at gaps that grow as the memory gets stronger. Doing that by hand is impossible with hundreds of words, so a scheduler does it.

## The scheduler: FSRS-6

BetterLang uses FSRS, the Free Spaced Repetition Scheduler, version 6. It is open source, and it came out of research that trained memory models on large sets of real flashcard answers ([Ye, Su & Cao, 2022](https://doi.org/10.1145/3534678.3539081); [Su et al., 2023](https://doi.org/10.1109/TKDE.2023.3251721)). Its authors publish an open benchmark of how well it predicts recall ([srs-benchmark](https://github.com/open-spaced-repetition/srs-benchmark)).

FSRS keeps three numbers for each Card:

- **Difficulty**, from 1 to 10: how hard this word is for you.
- **Stability**, in days: how long until your chance of recalling it falls to 90%.
- **Retrievability**: your chance of recalling it right now. It falls as time passes.

After every answer, FSRS updates the difficulty and the stability. It then sets the Card's next practice time for the moment your chance of recall is predicted to fall to the target you chose.

BetterLang's engine is a line-for-line port of the reference implementation, [py-fsrs](https://github.com/open-spaced-repetition/py-fsrs), checked against answer histories that py-fsrs itself produced. FSRS-6 has 21 parameters, and everyone uses the published defaults for now.

## Your answer, in FSRS terms

| You press | FSRS reads it as | What happens next |
|---|---|---|
| Yes | Good | Stability grows, and the next practice is further away. |
| Almost | Again | A miss: the Card comes back soon and is learned again. |
| Not at all | Again | A miss: the Card comes back soon and is learned again. |

"Almost" counts as a miss because FSRS models one thing: whether the recall happened. A word you nearly had is a word you could not use yet.

## A new word's first steps

- A new word comes back after 1 minute, then after 10 minutes, inside the same session.
- A known word you miss comes back after 10 minutes, then rejoins the longer gaps.
- Each gap is spread a little at random, so Cards learned together do not all come back on the same day.

## Choose how much you want to remember

The **Spacing** setting is the target recall: the share of words you should still remember when they come back.

| Setting | Target recall | Trade-off |
|---|---|---|
| Closer | 95% | The most practice. Almost nothing slips. |
| Standard (default) | 90% | FSRS's default balance. |
| Wider | 85% | Less practice, a few more misses. |
| Widest | 80% | The least practice. The lowest target the FSRS authors recommend: below it, forgetting costs more time than the spacing saves. |

## How many new words a day

BetterLang introduces at most **10 new words a day** by default; you can choose 0, 5, 10 or 20. Every new word adds practice in the days that follow, so a steady intake keeps each day's practice about the same size.

## What "Ready" means

A Card is **Ready** when its next practice time has come. Practice shows your Ready Cards, then new words up to your daily allowance. If you skip a few days, your Ready Cards wait for you, and FSRS uses the real time since your last answer, so a late answer still updates the memory correctly.

## Recognition first, then production

- While a word is new, you see the word and recall its meaning.
- Once it is familiar, you see the meaning and the sentence with the word blanked, and recall the word itself.
- Typing asks you to write it, accents included, or to say it with your device's dictation.

Recognising a word is easier than producing it: of four ways of testing word knowledge, recalling the word from its meaning was the hardest ([Laufer & Goldstein, 2004](https://doi.org/10.1111/j.0023-8333.2004.00260.x)). So production comes once recognition is secure.

## Which sentence you see

- **While a word is new,** its Flashcard shows the same sentence every time. One consistent context helps the early learning of a new word ([Mak, Hsiao & Nation, 2021](https://doi.org/10.1016/j.jml.2020.104203)), and adults recalled more of a new word's meaning after meeting it in one coherent story ([Hulme et al., 2023](https://doi.org/10.3758/s13423-023-02316-z)).
- **Once you know it,** each session shows the sentence you saw longest ago. Varied contexts help a known meaning carry over to new texts ([Bolger et al., 2008](https://doi.org/10.1080/01638530701792826); [Norman et al., 2023](https://doi.org/10.1177/17470218221126976)), though the effect is small.
- **Saved from only one sentence?** Once you know the word, up to three sentences that use it are found in your own Library, marked "From your Library".
- **Deleted a sentence?** It is gone for good, including from the Library search.

## Only real recall changes a Card's schedule

- Flashcards and Typing change a Card's schedule.
- Sentence practice has its own FSRS schedule for each sentence. A sentence answered right on the first try counts as Good; anything else as Again. Once a sentence is stable for about three weeks, you type or dictate the whole sentence instead of ordering tiles.
- Audio Drill's active recall has its own drill schedule.
- Writing and the AI chat tutor never change any schedule.

That keeps each memory model honest: a word's schedule reflects recalling that word, not unscrambling a sentence it appears in.

## Where the evidence stops

- FSRS's default parameters were fitted on flashcard data from many learners. They are not yet fitted to you; that needs a few hundred of your own answers, and it is planned.
- Sentence schedules use the same defaults, although they were not fitted on sentences. We watch first-try accuracy and adjust.
- No study has tested BetterLang itself.

## Questions

### Which spaced repetition algorithm does BetterLang use?

FSRS-6, the open-source Free Spaced Repetition Scheduler, with its default parameters, ported line for line from the reference implementation py-fsrs.

### Why does "Almost" count as a miss?

FSRS models whether a recall happened. A near miss means the word is not usable yet, so it comes back soon.

### What happens if I skip a few days?

Your Ready Cards wait for you. FSRS uses the real time since your last answer, so a late answer still updates the memory correctly.

### How much should I practise each day?

A little every day works better than a lot at once. New words are capped at 10 a day by default, and 15 answers a day keep your streak.

### Can I make words come back more or less often?

Yes. Settings has a Spacing option: Closer (95% target recall), Standard (90%, the default), Wider (85%) and Widest (80%).

## Sources

1. Bolger, D. J., Balass, M., Landen, E., & Perfetti, C. A. (2008). Context variation and definitions in learning the meanings of words: An instance-based learning approach. *Discourse Processes*, 45(2), 122–159. https://doi.org/10.1080/01638530701792826
2. Cepeda, N. J., Pashler, H., Vul, E., Wixted, J. T., & Rohrer, D. (2006). Distributed practice in verbal recall tasks: A review and quantitative synthesis. *Psychological Bulletin*, 132(3), 354–380. https://doi.org/10.1037/0033-2909.132.3.354
3. Cepeda, N. J., Vul, E., Rohrer, D., Wixted, J. T., & Pashler, H. (2008). Spacing effects in learning: A temporal ridgeline of optimal retention. *Psychological Science*, 19(11), 1095–1102. https://doi.org/10.1111/j.1467-9280.2008.02209.x
4. Ebbinghaus, H. (1885). *Über das Gedächtnis: Untersuchungen zur experimentellen Psychologie.* Duncker & Humblot. English translation (1913): *Memory: A contribution to experimental psychology.* Teachers College, Columbia University. https://doi.org/10.1037/10011-000
5. Hulme, R. C., Begum, A., Nation, K., & Rodd, J. M. (2023). Diversity of narrative context disrupts the early stage of learning the meanings of novel words. *Psychonomic Bulletin & Review*, 30(6), 2338–2350. https://doi.org/10.3758/s13423-023-02316-z
6. Karpicke, J. D., & Roediger, H. L., III (2008). The critical importance of retrieval for learning. *Science*, 319(5865), 966–968. https://doi.org/10.1126/science.1152408
7. Kim, S. K., & Webb, S. (2022). The effects of spaced practice on second language learning: A meta-analysis. *Language Learning*, 72(1), 269–319. https://doi.org/10.1111/lang.12479
8. Laufer, B., & Goldstein, Z. (2004). Testing vocabulary knowledge: Size, strength, and computer adaptiveness. *Language Learning*, 54(3), 399–436. https://doi.org/10.1111/j.0023-8333.2004.00260.x
9. Mak, M. H. C., Hsiao, Y., & Nation, K. (2021). Anchoring and contextual variation in the early stages of incidental word learning during reading. *Journal of Memory and Language*, 118, Article 104203. https://doi.org/10.1016/j.jml.2020.104203
10. Murre, J. M. J., & Dros, J. (2015). Replication and analysis of Ebbinghaus' forgetting curve. *PLOS ONE*, 10(7), e0120644. https://doi.org/10.1371/journal.pone.0120644
11. Norman, R., Hulme, R. C., Sarantopoulos, C., Chandran, V., Shen, H., Rodd, J. M., Joseph, H., & Taylor, J. S. H. (2023). Contextual diversity during word learning through reading benefits generalisation of learned meanings to new contexts. *Quarterly Journal of Experimental Psychology*, 76(7), 1658–1671. https://doi.org/10.1177/17470218221126976
12. Open Spaced Repetition. *py-fsrs*: the reference Python implementation of FSRS, version 6 (MIT licence). https://github.com/open-spaced-repetition/py-fsrs
13. Open Spaced Repetition. *srs-benchmark*: an open benchmark of spaced repetition algorithms. https://github.com/open-spaced-repetition/srs-benchmark
14. Roediger, H. L., III, & Karpicke, J. D. (2006). Test-enhanced learning: Taking memory tests improves long-term retention. *Psychological Science*, 17(3), 249–255. https://doi.org/10.1111/j.1467-9280.2006.01693.x
15. Su, J., Ye, J., Nie, L., Cao, Y., & Chen, Y. (2023). Optimizing spaced repetition schedule by capturing the dynamics of memory. *IEEE Transactions on Knowledge and Data Engineering*, 35(10), 10085–10097. https://doi.org/10.1109/TKDE.2023.3251721
16. Ye, J., Su, J., & Cao, Y. (2022). A stochastic shortest path algorithm for optimizing spaced repetition scheduling. *Proceedings of the 28th ACM SIGKDD Conference on Knowledge Discovery and Data Mining (KDD '22)*, 4381–4390. https://doi.org/10.1145/3534678.3539081