That is rather insulting to teens to say that they can't learn to dress appropriately for different situations unless you are told how to dress.
Dress codes work in some places, but lack of dress codes are also extremely effective in other places. I prefer my children learning how to make their own decisions on how to dress appropriately rather than having an administrative staff dictate how they are going to dress. The students still suffer the consequences if they show up in pasties and thongs.
You live in the deep south right? Traditionally, it is a much more conservative area of the country than say the West. I live in an area that has throughout its history been rather progressive in dress and style. So, different things work for different people. In my neck of the woods, first and second graders are dying the tips of their hair pink, blue. I was doing recess duty last week and a second grader came to school with bright purple hair. Because it is so prevalent, hair color and piercings do not hinder most adolescent type jobs around here. It is amusing to count piercings when checking out at the grocery store.