Spaced Repetition for Language Learning

You learn a word, feel good about it, and two weeks later it's gone. That cycle is frustrating, and it's not a personal failing. It's how memory works. Without review at the right time, most new vocabulary fades within days.

Spaced repetition fixes the timing problem. Instead of reviewing everything on a fixed schedule, it shows you each word right before you'd normally forget it. Langadoo uses the SM-2 algorithm to do this automatically with vocabulary you collect from real videos and texts.

In the 1880s, Hermann Ebbinghaus ran memory experiments on himself and mapped what he called the forgetting curve: new information decays quickly at first, then levels off. If you review something just as it's about to fade, the memory lasts longer next time. Review it again at the right moment, and it lasts even longer.

Spaced repetition systems (SRS) automate this. When you learn a new word, the system schedules a review soon, maybe the next day. If you remember it, the gap before the next review gets longer. If you forget, it comes back sooner. Over time, easy words almost disappear from your review queue, and hard ones keep showing up until they stick.

Here's a short video that explains the concept well:

SM-2 was created by Piotr Wozniak for SuperMemo in 1987 and is the same algorithm Anki uses under the hood. It's simple: after you see a word, you rate how well you remembered it. Langadoo gives you four options: again, hard, good, or easy.

Based on your rating, the algorithm adjusts two things: the interval before your next review, and an "easiness factor" for that card. Words you consistently get right spread out to intervals of days, then weeks, then months. Words you miss get reset to short intervals.

The practical effect is that your daily review session stays short even as your total vocabulary grows. You spend most of your time on words that actually need attention, not re-confirming things you already know well.

Most SRS tools start with an empty deck and expect you to type in your own cards. Langadoo works differently: you collect vocabulary while watching YouTube videos or reading texts, and those words go straight into your review queue with translations and audio already attached.

When you review, you can practice in both directions: seeing the target language and recalling the meaning, or seeing your native language and recalling the word. Both modes use the same SM-2 scheduling.

Words you save also stay highlighted in future videos and stories, so you see them in new contexts over time. That repeated exposure in different situations is what moves a word from "I've seen this before" to "I can actually use this."

The system works for any language and any script. Whether you're learning Korean, Arabic, or Finnish, the same tools apply. If your review queue gets too large, you can pause new cards and work through the backlog at your own pace.

Regular flashcard apps show you the same cards on a fixed schedule or in random order. You end up reviewing words you already know while the ones you're about to forget sit at the bottom of the deck.

There's also the context problem. A card that says "correr = to run" doesn't tell you how the word behaves in a sentence, what prepositions go with it, or what register it belongs to. You might recognize it on a card but blank when you hear it in conversation. That gap between recognition and recall is where most learners get stuck.

Some apps try to compensate with streaks and XP, but those are motivation tricks, not memory techniques. You can maintain a 200-day streak and still not remember the words from week one. Spaced repetition addresses the actual forgetting problem instead of papering over it with game mechanics.

A 2006 meta-analysis by Cepeda et al., published in Psychological Bulletin, reviewed 254 studies and found that spaced practice consistently outperformed massed practice (cramming) for long-term retention. The effect held across age groups, materials, and task types.

For language learners specifically, this means you remember more words with less total study time. Instead of grinding through a 500-word review session once a week, shorter daily sessions of 10-15 minutes produce better retention. The algorithm handles the scheduling; you just show up and work through what's due.

The other practical benefit is that your review queue gives you an honest picture of where you stand. You can see how many words you've learned, how many are due for review, and which ones you keep forgetting. That feedback loop is useful for adjusting your study habits.

SRS works well for anyone building a large vocabulary over months, but it's especially useful if you're studying on your own without a teacher setting the pace. If you only have 15-20 minutes a day, spaced repetition makes sure those minutes go toward the words that need the most attention.

It's also a good fit for people learning multiple languages at once, since you can maintain separate review queues without the schedules interfering. And if you're preparing for a proficiency exam, an SRS deck built from real content gives you vocabulary in context, which is closer to how test reading passages actually work.

If you want to dig into the science yourself, these are the studies most relevant to how spaced repetition systems like Langadoo schedule reviews.

• Ebbinghaus, H. (1885). Memory: A Contribution to Experimental Psychology. This classic work introduced the forgetting curve, showing how memory decays over time without review. Read more
• Cepeda, N. J. et al. (2006). "Distributed practice in verbal recall tasks." Psychological Bulletin, 132(3), 354–380. A large-scale review demonstrating that spaced practice outperforms massed practice for long-term retention. View article
• Kornell, N. (2009). "Optimising learning using flashcards." Applied Cognitive Psychology, 23(9), 1297–1317. Explores how to use flashcards and spacing strategies more effectively, supporting the principles used in modern SRS tools. View article