I don't think you are giving 6th grade boys enough credit. As mentioned, we don't have a dress code. We have girls in short shorts and camisoles all the time. At our splash days, girls are in bikinis, sometimes a bit skimpy and boys wear their speedos from swim team.I think crying "sexist" over the wording is the same as crying "bully" because someone says something not so nice too you. 6th grade boys have raging hormones, so while some women (even their mother's) may not like to hear it, the truth is, half dressed girls are going to be a distraction to some of those boys. Its nobody's fault, it is just the facts. Not stating that in the handbook doesn't really change that.
Oh, and half dressed boys will be a distraction too, but again the fact is that compared to the way girls dress, boys are generally more covered up. Anyone who has been in a school in the last 10 years knows this, admitting it doesn't make you sexist.
And yet, academically, it seems all those boys are just fine keeping their concentration in school as the school is ranked #1 in the state. And it is not just based on test scores, which the DIS knows is not accurate. The students win statewide math olympiads, science fairs, spelling bees, geography bees and Destination Imagination.
Boys being sexually distracted by a spaghetti strap is just a myth.