If you have imported students to your account, but have not enrolled them in a class, they will see the following message:
"You are currently not assigned to any classes. Please speak to your instructor to either open up classes for you to join, or assign you to a class."
After you import students to your account, you need to enroll them in a class. Once you do that, your students will be able to start practicing.
Go to the Classes tab. All of your classes should be visible on this screen.
Click the name of your class to be taken to the overview of the class. Click on "Student Enrollment." On this page, you can enroll students in your class by clicking the "Add existing students" button.
Before your students can start typing, you must enroll them in a class.