Administrator: How to specify which grades are visible to students and parents?

Access the Terms in the Grade book settings.

You can specify which grades are to be shown to parents and students. If you want to keep certificate grades hidden, just leave the corresponding box unchecked.
0: This is a pre-requisite to displaying grades as such
1: This will display intermediate grades, in other words common grades received during the term.
2. This will display information about awarded half-term grades
3. This will display information about end-term grades to be printed on end-term certificate

If a grade has been awarded and after that you restrict displaying grades to students/parents, the student/parent still receives a message about the new grade as it was sent immediately after the grade has been awarded.

The details of the grade will not be visible.