How Babbel and Duolingo Teach: 7 Science-Backed Principles
In short: Babbel and Duolingo teach millions of people languages, and their methods are publicly documented. Behind them sit 7 principles from learning science: reviewing right before forgetting, small portions, using words immediately, producing instead of recognizing, discovering patterns, treating mistakes as learning moments and daily motivation. These principles work for children too, ideally wrapped in real conversations instead of flashcards.
When we built the learning system behind Plaudan Kids, we took a close look at the two most successful language learning companies in the world: Babbel's didactics team has described its method in a dedicated paper, and Duolingo has published its learning science in a method whitepaper. The good news: both rely on the same principles that researchers have studied for decades. In this post we walk you through the 7 most important ones, how to spot them in any app, and how we implemented them for children between four and nine.
Why look at Babbel and Duolingo at all?
Because neither company guesses, they measure. Duolingo's whitepaper describes hundreds of A/B tests running every week across millions of learners, and Babbel employs its own didactics team of linguists. Whatever sits inside these apps has passed a double filter: learning research and practice with millions of real people. For you as a parent, these principles make a wonderful checklist, whichever app or method you choose in the end.
The 7 principles at a glance
1. Review right before the brain forgets
The most powerful principle is spaced repetition. Without review, a new word fades within days, as memory researcher Hermann Ebbinghaus first showed with his famous forgetting curve. The fix: review the word exactly when it is about to tip. Babbel uses six knowledge levels for this, with gaps growing from one day to six months. Duolingo goes further and predicts for every single word when it will be forgotten. At Plaudan, Leo remembers every word your child has been able to say and brings it back into the conversation when it is due: as a little riddle or game, never as a quiz.
2. Small portions instead of vocabulary lists
Working memory can only hold a handful of new units at a time. That is why Babbel always introduces new words in groups of three to four from one shared topic, and why Duolingo keeps its lessons down to a few minutes. More at once feels like more learning, but less of it sticks. A conversation with Leo therefore carries about three to four new words, spread across the whole chat, each inside its own little moment.
3. Use new words in real context immediately
A word that only lives on a flashcard stays theory. Babbel puts new vocabulary straight into everyday dialogues where it is actually needed. The technical term is the communicative approach: you learn language for situations, not for lists. In a conversation with Leo this happens automatically, because a conversation has no other place for a word than context: the new word appears inside a little story, your child uses it right away in an answer, and it comes up once more later that day.
4. Say it yourself instead of just recognizing it
Researchers call it the testing effect: what you retrieve from memory yourself sticks many times better than what you merely recognize. Seeing four pictures and tapping the right one is recognition. Saying the word out loud is retrieval, and retrieval is what builds language. Both big apps include speaking and writing exercises for exactly this reason. Plaudan takes the principle to its logical end: there is nothing to tap, your child says every word out loud, because only that counts. Why this matters so much to us is the topic of Why Kids Learn Languages by Speaking, Not Tapping.
5. Discover patterns instead of memorizing rules
Duolingo's core principle is implicit learning: instead of explaining grammar rules, the app shows carefully built example sets in which the brain discovers the pattern on its own. That is exactly the ability every child used to learn their native language, without a single rule. Children are world champions at it. Leo does the same: two or three examples that differ in exactly one spot, then your child gets to guess how the next one goes. The rule is named in one short sentence afterwards at most, and often not at all.
6. Mistakes are the beginning, not the end
When an exercise goes wrong, Duolingo brings it back at the end of the same lesson, so the lesson ends with a success. Research calls this desirable difficulty: a task just past the comfort zone that succeeds on the second try cements learning better than ten easy wins. Leo keeps it the same way: a word that did not work out is not ticked off, it returns later in the conversation in new packaging, so your child ends the day with that word as a win.
7. Showing up is half the language
Duolingo dedicates a whole chapter of its whitepaper to motivation, because the most common way to not learn a language is to stop. Streaks, collecting mechanics and small celebrations are not gimmicks, they are the reason tomorrow's practice happens. That is why Plaudan has the day streak and the treasure chest: every word your child has said becomes a treasure they can look at anytime. We draw the line somewhere else: the strongest reason to come back should be the friendship with Leo, not the score.
How do the three apps implement the principles?
| Principle | Babbel & Duolingo | Plaudan Kids |
|---|---|---|
| Spaced repetition | Flashcard trainer, review lessons | Leo brings due words back into the conversation |
| Small portions | 3 to 4 words per unit, short lessons | 3 to 4 new words per conversation |
| Context | Scripted dialogues to read and listen to | Real conversation, the word is needed right away |
| Active recall | Tap, write and speak exercises | Speaking only, every word said out loud |
| Pattern discovery | Example sets inside exercises | Examples in conversation, the child guesses on |
| Handling mistakes | Task returns at the end of the lesson | Word returns later, wrapped in a new game |
| Motivation | Streaks, points, leaderboards | Streak, treasure chest, friendship |
What do we deliberately do differently?
The honest part: Babbel explicitly targets adults, and Duolingo relies on reading and tapping, which works beautifully from school age on. For children between four and nine, neither fits, many of them cannot read yet. So we translated the same science into the only medium that truly carries at this age: spoken conversation. Your child experiences no lessons, no flashcards and no progress bars, they chat with a friend. That six review levels and a vocabulary curriculum run underneath is something they never notice. How that feels in a direct comparison is the topic of Plaudan vs Duolingo for kids.
What does it come down to?
The science behind Babbel and Duolingo is not a secret, it is a checklist. When you evaluate a learning method for your child, ask these four things: Does it review words on a schedule before they are forgotten? Does it portion small? Does my child have to speak instead of just tapping? And will my child want to come back tomorrow? Any method that gets four yeses will work. Best of all is when your child notices none of it, because they are simply having a good conversation.
Just try it out
Let your child experience what learning science feels like when it is hidden inside a friendship. Ad-free, no trackers, no hidden purchases, with a parent dashboard and one subscription for the whole family, already trusted by over 40,000 families.
Frequently asked questions
What is spaced repetition, in simple terms?
Spaced repetition means reviewing a word right before your brain would forget it. The gaps grow with every successful review, for example from one day to four days, a week and eventually months. That is how a word moves step by step into long-term memory.
Does Plaudan use the same method as Babbel and Duolingo?
Plaudan builds on the same learning science principles, such as spaced repetition, small learning portions and active recall. The difference is the packaging: instead of flashcards and typing exercises, everything at Plaudan happens invisibly inside a real spoken conversation with an animal friend.
Does the Babbel method work for children too?
The principles behind it apply to every brain, but Babbel itself explicitly targets adults and relies on reading and writing. Children between four and nine learn best through listening and speaking, so they need an implementation that works without reading.
How many new words should a child learn per day?
Fewer than many parents think: three to four new words per session is ideal, because working memory can only hold a few new units at once. What matters more than quantity is that the words come back before they are forgotten.
Why does my child forget words they already knew?
That is completely normal and has a name: the forgetting curve. Without review, a new word fades within days. The solution is not longer study time but planned review at growing intervals until the word truly sticks.