I love the feature " Mark cells as ......" I really like using the Mark cells as missing. It is my way of "locking assignments" in the gradebook book while still allowing some students to submit late. It alerts me, the kids, and the parents when I student didn't attempt an assignment.
However, there have been plenty of times where I have hit the wrong mark. I then had to go through and individually had to click on each one to get rid of it. There have been plenty of times were I have marked the cells a missing on the wrong assignment as well. I have also have had to clear all the marks on an assignment that I later extended for more time. This is very time consuming.
Having an option to clear all marks would be a great time saver. Please consider.