Note: we strongly recommend you begin the semester with the Course total hidden from students, to prevent worry over a low-seeming grade that results from very little coursework having been completed early in the semester. Remember, this hides ALL of the grades, not just a single item, and will have to be undone before you can hide some grade items but reveal others.
Go to your course site and, in the Administration menu on the left, select Grades.
In in the grade report page that appears, use the drop-down menu to select Gradebook Setup.
Find the line for the grade item you would like to hide, and click the Edit button for that line.
A pop-up menu should provide the option to Hide the grade: click Hide.
Scroll to the bottom of the screen and click on Save Changes.