I am a teacher and I set up classes and assignments for my students. However, they are completing other assignments that I did not assign and can't see the ones I did. Is there a way to limit their access?
This happened to me a few months ago, Mrs. Peters. We were getting ready to play restaurant in class: we had chosen who would be waiters and who would be customers, we named our restaurant, we decided on what food we would prepare and bring in, I unlocked all five of the restaurant skills, and I started each class with a beautiful note on the board that said, "Choose which restaurant skill you want to do while I take attendance." And then we worked on restaurant vocabulary and grammar skills for the rest of the class period, and talked about food. And then daily I reminded them that their assignment was to finish one of the restaurant skills. And yet, I had one student who completely ignored me and did something else entirely. Because he wasn't doing restaurant vocabulary outside of school (and honestly he wasn't very engaged in class), none of it was in his long-term memory. He didn't do very well when the big day came (That was their test, to order food in our pretend restaurant and sustain a conversation for 40 minutes). I figured that his failure on the test was lesson enough. After that, he listens to me more and follows instructions. And he is e-mailing me almost daily now that school is shuttered.
I am going to suggest that these are crazy times. Put the message out there constantly to your students that this is the assignment you want them to do (Duolingo sends them an e-mail; the students won't see it on the website). But you can be posting it on whatever social media you have, whatever on-line class tools are available to you, and e-mailing it to your students just to make sure they get the message. But if the students do something completely different, just take a deep breath, smile to yourself, and say, "Thank goodness; at least they are studying."
I am sorry that this is the best advice I can give you right now. Hang in there, and keep posting questions! We all need to support each other.