This can occur when the teacher is viewing their My Day page outside of the dates for a Marking Period.

As an example, the current date is 11/4/2017 and a teacher goes to view My Day > Schedule & Performance. 
The first quarter marking period ended on 11/3/2017, and the second quarter does not begin until 11/6/2017. 
Because the date is between marking periods, the Grade Book box would not display.