Since 2013, I have been using Duolingo as a free language-learning tool for student enrichment in my World Language course. I assign students homework under the Duolingo format each week, either through the free Duolingo Application or on the Duolingo Website.
In a 2012 study by R. Vesselinov and J.Grego, it was found that a person with no knowledge of Spanish would need between 26 and 49 hours (34 on average) to cover the material for the first college semester of Spanish.