It is nice to use the Assessment feature as a way to assess student understanding of assignments such as reading comprehension. The only problem is that once the due date occurs, each student who did not take the assessment must be 'unlocked' in order to complete the assignment.
Teachers have to extend the publish date for the student to go back in and be able to submit it late. The student should be able to submit it late and then have the assessment flagged as late, not on time or extended times.