Hi Tom,

Once students have already taken the diagnostic quiz, I don't believe that they are able to take it again. However, students should be able to work on any of the exercises in the Practice tab, even if they've already completed them. Students can also reset the practice tests and re-take them if they've already done all of the practice tests.

If you have a student that has already done some practice but is wanting to completely restart, they would need to create a new account.

Hope this helps! Let me know if you have any further questions!