The story behind DuoLingo
This article from the Carnegie Mellon University newsletter explains Duolingo in some detail: http://www.cmu.edu/homepage/society/2013/fall/app-of-the-year.shtml?utm_source=Newsletter_medium=Email_content=January_campaign=Newsletters
An interesting article and shows that DL has a strong academic background and not just a fly by night game. Well done all at DL, Luis et al. May the force stay with you.