I think this MIGHT be a work around to a problem I am having. I have unit quizzes the students take for practice (no credit) BUT I want them to look/feel/function just like the for credit quizzes (exams) in terms of all of the settings. Making them Practice Quizzes doesn't let me set them up exactly like the exams, so they are set as Graded Quizzes. I created an assignment group for just these practice quizzes and then dropped all of them (12 in total). I dropped both the 12 lowest and the 12 highest. It seems like this should drop every one of these from the calculated total grade but it doesn't seem to be working. I did this same thing for two Orientation assignments and it worked but can't seem to get it working in this assignment group.
With the assignment group, have you set the "% of total grade" to be 0? This should not allow the quizzes to be included in grade calculations but still let students see their "mark" for each quiz and an overall percentage for the assignment group. This can be set from the three dot menu at the right hand side of the assignment group header -> Edit.