As a child of the 60's, I am all about in freedom of expression, and I totally get why the kids are all abuzz about being told what they can and cannot wear! That said, I am going to make an argument in support of the dress codes for our students.
My views have their roots in the science of attraction and adolescent development. We know a couple of things, that human males are stimulated by visual cues and that adolescents are in the midst of developing into sexually mature humans, and are coming to terms with the many changes taking place within them. They are experiencing sexual attraction for the first time in their lives.
This is a really good reason to have dress codes in place in schools. Less revealing clothing will be less distracting to our kids, and they will be better able to focus on learning. Lets face it, that algebra equation is far less attractive than the glimpse of a bra strap or a six pack set of abs. Lets minimize the distractions and focus on the learning. (yep, I could even support a school uniform for similar reasons!)
As a parent I realize I need to teach both my son and daughter how to handle their sexuality. Part of that will be about how they feel about themselves, and part of it will be helping them understand how they may impact others. How they act, dress, and carry themselves will greatly impact how they are perceived and how others treat them. By understanding this, they can make informed decisions about how they present themselves, and how they react and interpret others they come into contact with.
It is my job to be sure they both understand the rules of consent. Outside of school, I want our youth to have the opportunity to experiment and explore how they express themselves. I want my children to understand that how someone dresses or acts does not reflect the kind of sexual attention they want. The only way that is expressed is directly, verbally, from someone old enough to give consent and someone not under the influence of drugs or alcohol. I want my children to judge people on who they are and how they act. I want them to avoid making snap judgement based solely on how someone dresses. At the same time I want them to understand that people may judge them on these things. Humans are visual creatures, and appearances to shape our perceptions and can lead to assumptions.
This is one of those parenting issues that is just filled with grey areas that I know will cause lots of family discussion and probably more than a little descent!