It's important to set this policy before you enter any grades. The grade posting policy allows you to determine when students see their grades.

This setting is located in the Grades area

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The default setting is automatically. Keep this if you want grades automatically shown to students.

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Select manually if you want to choose when students can see their grades.

This policy applies to individual assignments. Go to settings --> more options if you want to hide the total course grade.
You can set this policy for all your assignments or set a policy for select assignments.