You learn a word, and a few days later it's gone. That's not a flaw in you; it's how memory works. Spaced repetition is the simplest, best-supported way to fight it: review each word just before you'd forget it, at longer and longer intervals. Here's why it works, how the schedule is set, and how to use it well.
Why we forget
In the 1880s, Hermann Ebbinghaus memorised lists of nonsense syllables and tested himself at different delays. He found that forgetting is fast at first, then slows down, the "forgetting curve", and that each review makes the next round of forgetting slower.
The spacing effect
Reviews spread out over time beat the same number of reviews crammed together. This is one of the most replicated results in memory research. A large review by Cepeda and colleagues (2006) pooled hundreds of experiments and found the benefit consistently, with the best gap between reviews growing as the time you want to remember for grows.
Retrieval, not rereading
Spacing works best combined with retrieval: trying to recall the answer before you see it. Karpicke and Roediger (2008) showed that testing yourself does far more for long-term memory than restudying the same material. A flashcard you have to answer beats a list you reread.
How the schedule is set: SM-2
Most spaced-repetition tools use a version of SM-2, an algorithm Piotr Wozniak published in the late 1980s for SuperMemo. After each review, you rate how well you remembered: forgot, hard, good or easy. Words you find easy come back after longer and longer gaps; words you struggle with come back sooner. The schedule adapts to each word and to you.
Using it well
- Review a little every day. Short daily sessions keep the pile from building up.
- Learn words in sentences. Echo de menos a mi familia ("I miss my family") is easier to recall, and more useful, than echar de menos on its own.
- Don't add everything. Keep the words you'll actually use; a flood of cards becomes a chore.
- Pair it with input. Spaced repetition keeps words alive; meeting them again in real content and using them when you speak is what makes them yours.
How Zollang does it
- One personal vocabulary. Every word from your lessons, podcasts, videos and Easy Reader pages goes into one place. Words you only heard aren't forced into your reviews; you choose which ones to learn.
- SM-2 scheduling. Each word comes back just before you'd forget it. You review with flashcards, multiple choice, listening or typing, and rate yourself from Forgot to Easy. Vocabulary review is always free.
- Tricky words. A word you miss three times in a row is flagged and gets its own review.
- Contextual review. Zollang writes a fresh story from the words you're learning; you reveal them one by one, then check yourself on exactly those words, so you practise recalling them in a new context, not just on a card (paid plans).
- Your learning day ends at 4 a.m., so late-night reviews count for the day you're in.
It works for every language Zollang teaches: English, Spanish, French, German, Japanese, Chinese, Italian, Portuguese, Korean, Russian, Turkish, Dutch and Luxembourgish, with more on the way. See also comprehensible input and the Zollang method.
Frequently asked questions
How often should I review?
A little every day. The schedule decides which words are due; your job is to show up.
Is spaced repetition enough to learn a language?
No. It keeps words in memory, but you also need lots of listening and reading, and speaking.
Should I make my own cards?
Making cards from your own content helps you remember why each word matters. Keep them to words you'll actually use.