Hi @joannawares,
Copies of projects act like snapshots of the parent project at the point in time when the copy was made. Any changes you make to the parent will only be applied to future copies (this is true for Assignments, also).
Depending on what you're trying to do, you might be able to have your students create new copies, or get the updated files to them another way. Can you describe a little more about how you want your students to use these projects?
Mel