ReCaptcha inventor Luis von Ahn introduced Duolingo in 2012, hoping to help users master a new language. In minutes a day, the app promised, you could learn English, Spanish, French, or German—no books required, no instructors. And all for free.
The pitch sounded convincing enough. But in the first year after its debut, Duolingo had a hard time persuading hopeful linguists to keep up with the lessons. For every eight users who downloaded and tried Duolingo, seven never returned.
So von Ahn set out with his developers to make the app as addictive as Candy Crush and other popular games—in a good way. The addiction Duolingo cultivates, he says, isn’t harmful in the way the World Health Organization says compulsive video-game playing is; the organization classifies excessive video-gaming alongside opioid or amphetamine abuse. Duolingo really is about self-improvement, von Ahn says—time otherwise spent playing games, on social media, or doing nothing, is applied to developing a skill. What’s so bad about that?
Good or bad, Duolingo’s addiction rate is way up. Next-day retention is 55 percent, up from 13 percent in 2012. “That’s about as good as a middle-of-the-road game,” von Ahn says. And with about 300 million users, Duolingo is the largest language-teaching company in the world, by user base.