Good evening Gary.
You may have already found an answer to your query - but I hope you will not mind if I add this [late] response.
The Gradebook offers the ability to factor those missing marks (or zeroes if you will) back into the score. You will find the option by the following route:
Settings → Grades - This will place you in the Grader Report View, where you will have a dropdown menu (or tabs) from which you choose: Categories and Items → Full View. The 6th column in this window is Aggregate Only Non-Empty Grades. You will notice that you have the ability to turn off "Aggregate Only Non-Empty Grades" for a particular category and for the entire course. (Proceed carefully here because I have not examined the math when this option is deselected.) The screen capture below shows where "Aggregate Only..." lives and I have also provided the text from the Moodle Gradebook FAQ, where a nice explanation is given.
The information below is extracted from: http://docs.moodle.org/23/en/Grades_FAQ#Step-by-Step_Explanation
My student completed only one activity out of 5, but his course total shows 100%. How do I show a more "progressive" course total?
- From the view menu in the gradeboook, select "Categories and items"
- At the top line there is a folder icon and an edit icon on the right, click the edit icon
- You'll then see the title "Grade category," the 3rd item is "Aggregate only non-empty grades."
- Uncheck this.
By default, only non-empty grades are aggregated, the others are ignored. However, you can change this setting as well as others that affect the course total, by turning "Editing" on in the grader report, and clicking the "Edit" icon next to the course category (the very top row of the grader report).
You can untick the box "Aggregate only non-empty grades" if you want to show a more "progressive" score for each student. Their empty grades will count as a 0 and will be counted in the course mean/total.
If you prefer to show a sum of points, rather than a percentage, you can change the course category's aggregation method to "Sum of grades".
End of Excerpt from Moodle Docs Gradebook FAQ.
I hope this information proves useful.
Michele Edwards, New York