Dropping the lowest Assignment score only works if you are using “Category Weights” to calculate the Final Grade.  If you use total points to calculate the final grade, you cannot use “Drop Score”.

2.Make sure you have your Grade Setup already done.  In Category Weights box, in the fourth column, Drop Low.  Click on the category you want the lowest assignment dropped from.  Then replace the 0 to how ever many assignments you want dropped.

4.  Click Save when you are done.