The really cool thing about DuoLingo is that it's founder, Luis von Ahn, is a native of Guatemala! If you have any Spanish students who are interested in coding, math, and computer science, check out the new podcast on my personal favorite podcast series with Guy Raz on NPR, "How I Built This."
Though I am not a big fan of DuoLingo for acquiring language, it certainly can be good for student practice on the go. Once you get beyond the semi-cringe-worthy errors that your students see with AI-created language technology, it is after all, a good, free tool for schools who can't afford other technology.
If your student does not want to listen to a one hour podcast (though I highly recommend it for Luis's great personality), here is a short article from the BBC.