They started off with a business model which entailed having users translate documents for partners. Last I read, they have pivoted to using ads and in app purchases, along with charging for certifications. I don't know whether or not they are turning a profit with these methods.
Facebook, Airbnb, Stripe, PayPal, Hulu etc are making money. I think the point is that if education is a good area for entrepreneurs to make money, there should be some example success stories already. So far, nothing worth mentioning in education segment.