If a student creates an individual account or is part of a different class, they can join your EEi class through the My Account section. There is a menu option called Join EEi Class. They can choose that and simply enter the School Code for your account.
You will want to delete the student profile you created in your account for that student (if you did so) as they will come in as a new student and having duplicates can be confusing and cause issues.