The Department Picker on curriculum pages can be organized by either department or grade level depending on how your School is set up. To find out how your school is set up:
Go into > Core > School > School & Grade Levels
Click the Edit icon for your School
On the General tab, it will have how your courses are organized. Courses are organized by department if not all courses are associated with a single grade level. Typically, Upper Schools are organized by department. Courses are organized by grade level if all courses are associated with only one grade level.