There is bug affecting changing the visibility of gradebook items via the Quick settings block that we will be fixing in the future. In the meantime you can accomplish this action via the regular Myplace settings. 

For the overall visibility of the Gradebook to students

You can do the same effect by going into the Class ADministration > Edit Settings > Appearance and setting "Show gradebook to students" to "No" (this is the "proper" way to do this):

For Individual Grade Items

The individual grade item visibility can be toggled via the Class Administration > Gradebook Setup:

The Edit > Show (or Hide) option in the menu for each grade item can be used to toggle the visibility of the grade item: