It's possible for a grade item to be visible to students even if its column hidden in the grade center. If the grade item is contained within a category, Exams or Assignments, for example, the aggregated score information may still be displayed to students by the category itself. To prevent this, follow the instructions in this guide.
Note: This must be set for each individual category and cannot be set as default behavior.
In your Brightspace course, click the Grades tab followed by Manage Grades.
For the category you wish to edit, select Edit from its drop-down menu.
In the Properties tab, scroll down to Display Options. Check Override display options for this item.
Uncheck all options listed under Show.
Click Save and Close.