Should you desire to have a firm due date for grade purposes, with the opportunity for students to continue to access the problems purely for practice, the following process will accomplish these goals.
Prior to doing the following steps, you should have in mind where you intend to place the practice assignments. They could reside next to the scored attempts, or could be grouped together in a review unit or folder.
Choose the Assignment option on the right of the assignment for which you would like create a practice version
Move assignment to desired location
The assignment will be created and placed at the top of the section you indicated. Click and drag it to your desired location.
It is important that a due date is associated with the assignment, or students will be unable to access the problems
If the purpose of creating this practice assignment is to allow students to practice before an exam, then the due date could be right before exam time.