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The intellectual foundation for flashcard-based learning was laid in 1885 by German psychologist Hermann Ebbinghaus, who published the first rigorous study of human memory. His central finding - the forgetting curve - demonstrated that without review, people forget roughly 50% of new information within a day and up to 90% within a week. More importantly, he found that each review at the right moment resets and flattens the curve, requiring progressively longer intervals before the next review.
In 1972, German science journalist Sebastian Leitner turned Ebbinghaus's research into a practical system using physical index cards sorted into five boxes. Cards answered correctly moved to the next box (reviewed less frequently); cards answered incorrectly returned to Box 1 (reviewed daily). This Leitner System became the standard study method in German schools and spread globally.
In 1987, Polish researcher Piotr Wozniak wrote the first computerised spaced repetition algorithm (SM-2), which formed the basis of his SuperMemo software. In 2006, the open-source application Anki made algorithm-driven spaced repetition accessible to everyone for free - and it became the dominant tool among medical students, language learners, and competitive exam aspirants worldwide.
Research consistently confirms that spaced repetition is 50-70% more time-efficient than equivalent time spent re-reading notes. The key variable is honest self-assessment at the moment of recall - rating a card as Easy when it was merely familiar is the most common mistake that undermines the technique.