In RenWeb(FACTS), we have the ability to fill in our student’s grades en masse. We choose the Auto Fill Grades button, and type in a grade (usually a 100%), and accept. It then fills in all student’s grades for the assignment with the grade we entered in. This is a very handy feature that has saved me a lot of time over the years.
Hmm, I suspect this may not already exist because it’s rare for students to all get the same mark on an assignment. The markbook does, however, support quickly entering grades by typing a number and hitting enter, and it will automatically select the next student, so you can fill grades faster without needing to use a mouse. Perhaps this helps?