The studies behind this app
What the studies say, and how we use them — in easy English.
This app helps you fix the American English mistakes you keep making, whatever your first language is. We did not just guess how to do that — we looked at real studies about how people learn a language, how they remember it, and why correct English matters. Here is what these studies say, and how we use them.
Why correct English matters
You can be very good at your job. But people read your English first — your emails, your messages, your work history. Small grammar mistakes can make your English look worse, even when your ideas are good.
A big study looked at almost 500,000 people who were looking for a job. The people with better writing got jobs more often — 8% more. And the people who got a job also got more money — about 10% more for each hour. Better writing did not make them look smarter than they were. It helped employers see how good they really were.
Employers say the same thing . 86 out of 100 say that bad writing makes you look worse when you ask for a job. More than half of them also look at your writing — both when they choose who to give a job to, and when they choose who to move up to a better job.
So correct English is not just something extra. When you fix the small mistakes, people can see how good you really are.
How we teach grammar
Most apps give you a rule and ask you to remember it. The studies show a better way.
First, you see it.
One big study looked at many other studies , with almost 700,000 learners. It found that clear grammar teaching works very well. But only telling you the rule is not enough. Another study tried two ways. When they only told people the rule, it did almost nothing. The real help came when people saw the grammar in real sentences. So this is where we start: first, you learn to see the correct form of the grammar rule — in real sentences.
Then, you use it.
Seeing a rule and using a rule are not the same thing. In one study , only the people who wrote their own sentences got much better at writing — not just reading. A study from 2025 found the same thing. Making your own sentences helps most with the English you use fast, when you have no time to think. So after you see the rule, we ask you to use it yourself. The more you use the correct form, the more it replaces the old habit.
Seeing and using train different things.
A review of 42 studies put these two halves side by side. Reading sentences and answering questions about them was the best way to learn to understand the grammar. Writing your own sentences was the best way to learn to use it — and both halves worked even better when learners got a clear explanation first. The two halves do different jobs, so you need both. That is why every lesson here has both: first questions about sentences, then sentences you write yourself.
Some questions are about you.
In the teaching method these studies tested, not every question has a right answer. Some questions ask about your own life — “I have worked with a difficult customer before: true for you?” There is nothing to get wrong. But to answer, your brain still has to process the grammar — and now it is connected to something you care about. We put these questions in every lesson. Give true answers; that is the whole exercise.
Keep it real.
This way of teaching has one big idea. You learn grammar best when you use it for something real — to say or understand a real thing. You do not learn it well when you only fill in empty exercises. That is why we use real examples from work and life.
How we help you remember
You can learn a rule today and forget it next week. That is not really learning. Three ideas from studies help us plan your practice.
Study again later — not all at one time.
A study of more than 26,000 working people found this: when you learn something and then come back to it later, you learn much more. You can also use it in new ways. And each time you repeat it, you have a better chance to remember it. So we bring each rule’s exercises back to you again and again.
Do different things together — not one at a time.
The first study to show this for language learning taught people two Spanish verb forms. The two forms were so close that people often used the wrong one. Some people learned them together. Other people learned one form at a time. In one day, learning them together did not help. But over a few weeks — the way you use an app — learning them together helped a lot in a later test. Why does this help with grammar? When you change from one form to another one that looks the same, your brain learns to see the difference between them. And most grammar mistakes come from this. So we give you different rules together in your practice.
Come back every day.
People who use Duolingo study more when they have a "streak" — the number of days you study with no break. It helps even more for people who do not stop. To remove old mistakes, you need to come back again and again. So we use streaks to help you do the most important thing: come back every day.
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Just 15–20 minutes a day, on the mistakes you really make.
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