Are you finished?

Are you finished?
 

Como se dice: " Are you finished?" (as in: are you finished with the assignment that you have been working on for the last 10 minutes?)

I have seen so many choices. I would just like one simple answer. One that you use in your classroom with your students.

Can you tell me how to say it to one student and to more than one student.

You can take a look at this thread to find some answers. :)