# Did you know ... spaced repetition was first applied using flashcards? LLM Brief Human page: https://drillster.com/en/blog/spaced-repetition-was-first-applied-using-flashcards ## Description What is spaced repetition and how Sebastian Leitner first applied it with flashcards. Discover the Leitner system, practical examples, and the science behind this study technique. ## Content # Did you know ... spaced repetition was first applied using flashcards? Imagine studying something for three straight hours. The next day, you remember most of it. But a week later, barely 10% remains. Cognitive psychology research has demonstrated this pattern again and again since 1885. In 1972, a German science journalist named Sebastian Leitner decided to do something about it. His solution was surprisingly simple: **a cardboard box divided into five compartments and a deck of handwritten flashcards**. That homemade invention became the first practical application of spaced repetition as a study technique, and its influence is still present in every modern learning application. ## What is spaced repetition _Spaced repetition_ is a study method based on a straightforward principle: **reviewing information at increasing intervals over time rather than cramming it all at once**. Instead of spending an entire afternoon memorizing a topic, you review it multiple times across days or weeks, leaving a longer gap between each session. The scientific foundation goes back to 1885, when German psychologist Hermann Ebbinghaus published _Uber das Gedachtnis_ (On Memory), the first experimental study of how we forget. Ebbinghaus memorized lists of nonsense syllables and measured how much he retained after 20 minutes, one hour, one day, one week, and one month. He found that **most forgetting happens in the first few hours**: roughly 70% of new information vanishes within 24 hours without active review. This pattern is known as the _forgetting curve_, and a [modern replication by Murre and Dros (2015)](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120644) confirmed that Ebbinghaus's findings still hold more than a century later. Ebbinghaus also discovered the remedy: **each review at the right moment flattens the forgetting curve**, allowing information to be retained longer with less total effort. The key is studying _when the timing is right_. ## The Leitner method: the first practical spaced repetition system Sebastian Leitner (1919-1989) was a science journalist: someone who knew how to translate research into something practical. In 1972 he published [_So lernt man lernen_](https://www.goodreads.com/book/show/6241069-so-lernt-man-lernen-der-weg-zum-erfolg) (How to Learn to Learn), a book that became a bestseller and contained the first structured method for applying spaced repetition to daily study. The _Leitner system_ works with a box divided into five compartments and cards with a question on one side and the answer on the other: - **Box 1**: new or missed cards, reviewed **daily** - **Box 2**: reviewed **every two days** - **Box 3**: reviewed **every four days** - **Box 4**: reviewed **weekly** - **Box 5**: mastered material, reviewed **once a month** The mechanics are elegant. When you answer correctly, the card advances to the next box, where it will wait longer before reappearing. When you get it wrong, the card returns to Box 1, regardless of where it was. The result is that **the cards you struggle with appear more often**, and the ones you've mastered appear less. The system automatically prioritizes your weak spots without you having to decide. That is exactly what spaced repetition as a study technique needs to work: adapting to what you _don't_ know. ## Why it works: the science behind the technique The Leitner method rested on solid principles. Cognitive psychology has confirmed at least three of them through decades of research. ### The spacing effect Reviewing information at increasing intervals produces significantly better retention than studying it in a single intensive session. A study by [Kornell (2009)](https://onlinelibrary.wiley.com/doi/abs/10.1002/acp.1537) demonstrated this directly with flashcards: **90% of participants learned more with spaced practice than with massed study**. Here's the striking part: 72% of those same participants _believed_ that massed study had worked better for them. Our intuition about how we learn frequently misleads us. ### Retrieval practice The act of trying to recall something, even if you fail, strengthens memory far more than simply rereading the material. The Leitner system forces you to actively retrieve the answer at each review. That effort of recall is precisely what anchors knowledge in long-term memory, a phenomenon researchers have named the _generation effect_. ### Desirable difficulties Robert Bjork, a researcher at [UCLA](https://bjorklab.psych.ucla.edu/research/), coined the term _desirable difficulties_ to describe study conditions that feel harder in the moment but produce more durable learning. Spacing is one of them: if a review feels too easy, it probably isn't doing much for your long-term memory. The difficulty of the effort signals that genuine learning is taking place. > "The timing of your review determines how much you retain long-term." ## Examples of spaced repetition in practice Spaced repetition is applied today across a wide range of contexts. Here are some concrete examples of how it is used for studying and maintaining professional competences: - **Language learners**: acquire vocabulary by reviewing difficult words daily and familiar words at decreasing frequency, automatically prioritizing what challenges them most - **Medical students**: memorize anatomy, pharmacology, and diagnostic criteria using apps like [Anki](https://apps.ankiweb.net/), which automate the Leitner system digitally - **Pilots and aviation personnel**: review emergency procedures and safety regulations periodically to keep their operational competence current - **Financial professionals**: keep their knowledge of regulations, compliance requirements, and complex products up to date in a constantly shifting regulatory environment - **Healthcare workers**: refresh clinical protocols, drug interactions, and patient safety procedures at optimized intervals In all these cases, the principle is the same one Leitner applied with his cardboard box: **what you don't know well appears more, what you've mastered appears less**. The principle remains the same as in 1972. What has changed is the scale and precision with which the _ideal review moment_ is calculated for each individual. ## From cardboard flashcards to adaptive algorithms Leitner's physical box worked well for a single person studying alone. But scaling the system to hundreds or thousands of professionals, each with different knowledge gaps, was impossible on paper. [Adaptive learning on a micro level](/en/blog/adaptive-learning-on-a-micro-level) takes Leitner's principle a step further. Drillster's algorithm determines for each person and each concept when the optimal moment to review has arrived, based on their individual response history. No two employees follow the same learning path, because no two people share the same gaps in knowledge and competences. **Completing a training course does not equal being competent.** The [forgetting curve](/en/blog/the-memory-paradox-why-memorizing-still-matters-in-the-age-of-ai) does not distinguish between students and seasoned professionals. What sets apart organizations that maintain reliable competences is that they have stopped assuming a single training session is enough: knowledge and competences need continuous maintenance, exactly as Leitner demonstrated with his five-compartment box over half a century ago. If you want to see how Drillster applies spaced repetition in your organization's context, [discover how it works](/en/what-is-drillster) or explore [how other organizations have tackled this challenge](/en/success-cases). --- _Want to make sure your team retains what they learn? [Book a demo with our team](/en/contact) and we'll show you how it works in practice._ ## References - Ebbinghaus, H. (1885) - _Uber das Gedachtnis_, translated as _Memory: A Contribution to Experimental Psychology_ [View text](https://psychclassics.yorku.ca/Ebbinghaus/index.htm) - Murre, J. M. J. and Dros, J. (2015) - Replication and Analysis of Ebbinghaus' Forgetting Curve, _PLOS ONE_ [View study](https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0120644) - Leitner, S. (1972) - _So lernt man lernen: Der Weg zum Erfolg_, Herder Verlag [View book](https://www.goodreads.com/book/show/6241069-so-lernt-man-lernen-der-weg-zum-erfolg) - Kornell, N. (2009) - Optimising learning using flashcards: Spacing is more effective than cramming, _Applied Cognitive Psychology_ [View study](https://onlinelibrary.wiley.com/doi/abs/10.1002/acp.1537) - Bjork, R. A. - Desirable difficulties in learning, UCLA Bjork Learning and Forgetting Lab [View research](https://bjorklab.psych.ucla.edu/research/)