By 2021 more people in the United States were learning languages on Duolingo than in all American high schools combined. The app came from a Carnegie Mellon professor and his Ph.D. student. It taught 40 languages to about 40 million monthly users in short, game-like lessons, nudged along by a green owl. Duolingo was free, and only about 5 percent of users paid. It went public in July 2021 from its home in Pittsburgh.

A Professor and His Student

Luis von Ahn grew up in Guatemala and became a computer science professor at Carnegie Mellon and a MacArthur Fellow. He founded Duolingo in 2011 with Severin Hacker, his Ph.D. student, and launched it in 2012. The bet was that free education could reach far more people than paid classes, if the product was fun enough to open every day. The team ran constant A/B tests. They lifted the share of learners who came back the next day from 12 percent to over 40 percent.

Paid Users, Then Profits

Duolingo added a paid tier, Duolingo Plus, in 2017. Paying subscribers grew from 0.9 million at the end of 2019 to 1.6 million a year later. The company priced its IPO at $102 a share in July 2021 and listed on Nasdaq as DUOL. It kept adding subjects, including math and music, and grew its paying base. Duolingo still trades on Nasdaq, with its headquarters in Pittsburgh.

Cover: Ornament with Owl Mocked by Day Birds, Master F.V.B.. Art Institute of Chicago, public domain. Chosen for an owl (Duo, the mascot).