Assignments for students who have already mastered content (add ability for teachers to see previous work before it was assigned)

I encourage my students to work through Khan at their own pace, but I periodically assign tests as checkpoints to monitor class progress.  Right now, if a student has already mastered the test or practice I assigned, there is no way for me as a teacher to see this unless they redo the assignment.  

I would love to see some type of indication for students who have already mastered it before I assigned it.  

Right now, I just have students show me their 100% and I make a mental note, but I would love to see a green check or something similar so I know students already mastered it before I assigned it.  Then I could still ask them to redo it, or simply have them continue "onward."  

I also posted this as help request #288644 and it was marked as solved so if this would be helpful to you and others, please reply or vote for it.