Aggregate only non empty grades certainly works for mean of grades (that is the average of percentages), simple weighted mean of grades (that is average of points), and Weighted mean of grades. Sum of grades would work the same whether you counted missing grades as zero or not.
Make sure you go through this tutorial as it shows the correct computations using Aggregate only non-empty grades.
But the short of it is that you should not have to put items into a zero weighted category. They are not factored into the grade until a grade is assigned (which could be zero or any other acceptable value).
Gary, Thanks so much for your reply. I watched the tutorial and changed the categories to simple weighted mean of grades (while leaving parent category as weighted). This now allows me to use aggregate only non empty grades. Another tutorial I saw told me to set categories to sum when using weighted. That option doesn't allow for aggregate only non empty grades apparently. http://tinyurl.com/5l6rbw
Would you say that is correct... one cannot use sum and weighted together if we want the non empty grade option?