Look at the dress code thread it is a bit long and starts out with codes for kids but moves to codes for teachers.
This is teaching not the business world. I think teachers should dress nice but there is no way i will wear a tie. It gets in the way. I wear the clothes that will stand up to the way i teach. I do not make enough money to buy new dress pants every couple of months, because I rip them crawling on the floor. My dress shirts get stained when experiments go awry, so I wear the most cost effective button down shirts I can.
I agree things can get pretty sloppy at times but for the most part I think teachers dress pretty well.