The Grade Book does look at the max points for the assignments when a teacher selects to drop lowest grades. It will drop the assignment with the lowest earned point value first but if there are 2 assignments with equally low point values (percentage wise) then it will drop the assignment with the lowest max point value first.  Meaning, if a Teacher selects to drop the two lowest grades and a Student has three 0s, for assignments that are worth 100, 50 and 25 points, respectively, the 0s for the 50 and 25 point assignments will be dropped. This is to keep important assignment grades from being dropped from the Grade Book.