If you are using Google Forms to track student progress, you might want the students to be changing their previously submitted responses versus submit the form all over again. This can also help to keep your spreadsheets with the responses from becoming overwhelming. If that is true for you, then here is a screencast to show you how to set it up as well as to have your students do it. Believe me, it's a lot easier than you think! And thank you to the teacher who asked me so that I figured this out, too.
I had a teacher ask me if there was a way to hide or remove students who are no longer in your class. The answer is maybe. It depends on if they are officially dropped from your class and appearing as red in your roster and gradebook. If not, then no, you cannot remove them until they have been unenrolled from the class. If the student is showing up as red in your gradebook though, you can hide them so you don't have to worry about them. Here is a screenshot to help you do it: