Yes, apparently this varied from area to area- as I noted jeans were taboo in my schools after 5th or 6th grade- same for shorts and sneakers (except for gym) but apparently in some areas these were ok right through high school. I feel cheated I didn't have this privilege. The fact that it varies from school to school and place to place shows that dress codes don't make sense- they just reflect the bias of whoever makes the rules.
As for your second point- I have a cartoon on my wall of a half-naked man confronting a waitress in a dinner- he's saying- "Your sign says
'shoes and shirt required'- doesn't say a thing about pants!"
