The science behind Hippo
The hippocampus — the brain's memory centre — is where long-term memories are formed. It's why we called this Hippo. We didn't invent spaced repetition. We just made it work inside real classrooms. This is why Hippo students retain more — without asking them to study harder.
Your brain forgets. Fast.
In 1885, Hermann Ebbinghaus discovered something uncomfortable: without active review, we forget most of what we learn — remarkably quickly. Within 24 hours, retention drops to around 50–60%. Within a week, as little as 25% remains. After two weeks, most of the original material has faded.
This isn't a flaw in how we learn — it's how memory consolidation works. The brain is efficient: it discards information that doesn't seem important. The trick is signalling importance through well-timed review.
Review at the right moment
Spaced repetition reschedules each card based on how well you know it. Cards you struggle with come back sooner. Cards you know well are spaced further apart. The result: you review everything just before you'd forget it — maximising retention per minute of study.
Each review doesn't just restore the memory — it strengthens it. The forgetting curve becomes shallower with each well-timed repetition. What initially required daily review might eventually need only monthly reinforcement.
Testing yourself beats re-reading
One of the most robust findings in learning science is the testing effect: actively retrieving information from memory produces dramatically stronger, more durable memories than passively reviewing the same material. Re-reading notes feels productive, but it mostly builds familiarity — not recall.
Roediger and Karpicke (2006) demonstrated that students who tested themselves remembered significantly more after one week than students who spent the same time re-studying. The effort of retrieval is what makes the memory stick.
Hippo is built around retrieval, not review. Every study session asks students to actively recall or apply what they've learned — never to passively re-read.
Reference: Agarwal, P.K. & Bain, P.M. (2019). Powerful Teaching. Jossey-Bass.
Better than Ebbinghaus
Hippo uses FSRS — the Free Spaced Repetition Scheduler — a modern algorithm trained on hundreds of millions of real study sessions collected from learners worldwide. It's more accurate than the SM-2 algorithm used by Anki and early versions of Quizlet.
Where older algorithms treat every learner the same, FSRS adapts to each individual. It predicts your personal forgetting curve for each card and schedules reviews at the optimal moment — the point where the effort of recall is highest but still achievable.
The result: students study less but remember more. FSRS minimises wasted review time while maintaining a target retention rate of 90%.
Not just memorisation
Most flashcard apps stop at simple recall: show a question, check the answer. Hippo goes further with two additional card types grounded in research.
Prediction cards ask students to make a prediction before seeing new material. This leverages the pretesting effect (Richland et al., 2009) — making a guess, even a wrong one, primes the brain to encode the correct answer more deeply.
Error identification cards present a statement or solution containing a deliberate mistake. Students must find the error — a task that requires genuine understanding, not just pattern matching. This targets misconceptions directly, helping teachers see not just what students don't know, but what they incorrectly believe.
Respecting your time
Hippo doesn't use streaks, guilt mechanics, or push notifications. There are no leaderboards outside of Live Mode, no daily reminders, no “you'll lose your progress” warnings. Every design decision is aimed at efficient learning, not engagement metrics.
We want students to use Hippo less, not more — because that means it's working.