Science of learning
Why it works.
Every rule in the game comes from more than a century of research on memory and learning, confirmed by meta-analyses published since 2020. Here we explain the seven principles the platform is built on, and the studies behind them.
Across 222 classroom studies with 48,478 students, quizzing raised academic achievement to a medium extent.
Seven principles, seven design decisions
01 · The problemForgetting curveForgetting does not follow a single curve: the rate changes over the first hours, the first week and beyond. And a group's average curve does not describe each person.In the game: questions come back before they are forgotten.02 · When to reviewSpaced repetitionA meta-analysis of 29 studies found a strong benefit from spacing out quiz sessions instead of running them back to back. Longer gaps work better when you need to remember later.In the game: a memory model per person and per question.03 · How to reviewRetrieval practiceA meta-analysis of 222 classroom studies with 48,478 students found that quizzing improves achievement to a medium extent.In the game: questions instead of summaries.04 · After answeringFeedbackA meta-analysis of 435 studies found a medium effect of feedback. Explaining the answer tends to teach more than just saying right or wrong.In the game: the correct answer and a short explanation, every time.05 · The right effortDesirable difficulties and interleavingMixing topics feels slower, but learning sticks better. In a physics course, interleaved practice improved scores on surprise tests, even though students thought they learned less.In the game: questions from earlier levels mixed in with new ones.06 · The formatPicture superiority effectPictures are remembered better than words, and recent studies explain this by distinctiveness. And placing picture and text together, without irrelevant detail, helps people learn.In the game: images in questions and in answers.07 · MotivationGamification researchFive meta-analyses published since 2020 found positive effects of gamification on learning. In an experiment, badges and leaderboards reinforced the sense of competence.In the game: levels, medals, leaderboards and challenges.
From research to screen
| What the research says | What the game does | Source |
|---|---|---|
| We forget what we do not review, at a rate that changes over time, and the group average is not each person's curve | Six questions a day instead of one long session | Radvansky and colleagues (2022); Murre (2023); Ebbinghaus (1885) |
| Spacing out quiz sessions gives a strong benefit, and longer gaps help you remember later | Each correct answer pushes the question's next appearance further away | Latimier and colleagues (2021); Kim and Webb (2022); Cepeda and colleagues (2008) |
| The memory half-life of each item can be estimated from the answer history | A memory half-life model per person and per question | Settles and Meeder (2016); Ye and colleagues (2022) |
| Quizzing improves achievement to a medium extent, in real classrooms too | Everything is question and answer | Yang and colleagues (2021); Agarwal and colleagues (2021); Roediger and Karpicke (2006) |
| Plausible alternatives can trigger productive retrieval | Believable wrong answers, checked against quality rules | Little and colleagues (2012) |
| Feedback has a medium effect, and explaining the answer teaches more than right or wrong | The correct answer and an explanation after every question | Wisniewski and colleagues (2020); Mertens and colleagues (2022); Butler and Roediger (2008) |
| Mixing topics improves memory and transfer to new cases | Questions from earlier levels mixed in with new ones | Firth and colleagues (2021); Samani and Pan (2021); Bjork and Bjork (2020) |
| Pictures are remembered better than words, and recent studies explain this by distinctiveness | Questions and answers with images | Higdon and colleagues (2025); Noetel and colleagues (2022); Paivio and Csapo (1973) |
| Gamification has positive effects on learning, and badges reinforce the sense of competence | Six medals, levels, leaderboards and challenges | Bai and colleagues (2020); Sailer and Homner (2020); Sailer and colleagues (2017) |