If the "Allow Teacher Grade Scale" option is checked for a course period, then teacher would be able to create his own custom grade scale for that particular course. However, for the other course periods where this option is not checked the scores would follow the grading scale created by the admin. This option allows the teacher to create a grade scale and students receive letter grades according to the scale created by the teacher.
To setup the teacher grade scale, go to Teacher portal >> Grades >> Setup >> Configuration.
Teacher Grade Scale :
This is the teacher’s own grade scale. This overrides the school’s grade scale.
Example: School has 90 and above for A. Teacher has 95 and above for A.
Then if a student gets 94, the letter grade should be B in that course period.