I have been learning Spanish with Duolingo for over six months now. It is a very convenient format, everything is in a game form, progress is tracked. But sometimes there are glitches: it does not count the correct answers or does not synchronize progress between devices. It turns out that this is not only me here, on https://duolingo.pissedconsumer.com/customer-service.html users also share similar problems. Overall, the service is excellent, but they definitely need to improve their technical support.