Can anyone think of any reasons why a student should not take AP Physics C before AP Chemistry if they haven't had a full high school level course in either?
In our local high school, there is a very practical reason not to take AP Physics before 12th grade. AP Physics requires a number of group projects, and the vast majority of students in the class are seniors. They stop caring about school after 1st semester.
Any junior taking the class would likely see poor grades on group projects, affecting his/her GPA during a critical year.