Duolingo for Schools. Within Duolingo for Schools teachers can create online classrooms in which they monitor their students' progression through the learning activities available in Duolingo.
To start off 2016 Duolingo introduced an assignment distribution option for teachers. Now teachers can set learning targets for students, give assignments, and track their students' progress through Duolingo for Schools. Students will receive notifications of new assignments when their teachers assign them.
In the video embedded below I provide a demonstration of how to create a classroom in Duolingo for Schools. The video also shows a student's view of Duolingo for Schools.