I work at a very poor, challenged middle school -- 81% free/reduced lunch, 30% of our students are in foster care with another 10%-20% being in some form of "alternative" family care (i.e., being raised by grandparents, older siblings, aunts or uncles, etc).
We don't have a uniform, but we do have a strict dress code -- boys have to wear their pants up -- not falling down off their bums with underwear showing, shirts must be tucked in. No drug or sexual innuendos on t-shirts. Girls can't wear heels higher than 1/2 inch (though that is mostly for safety as we are an outdoor campus and the students walk across sand/grass a lot) and their skirts can't be any higher than 4 inches above the knee. Also, no midriff shirts or spaghetti strap tanks. Students breaking dress code in our school have been put in ISSP until a parent or guardian can bring appropriate clothes to wear.
My favorite days are game days -- when the sports team (whether it's football, soccer, basketball, baseball) is required by coaches to wear dress slacks, button down shirts and ties (for boys) or nice pants/skirt and nice shirt or dress (for girls). Not only do the children look fantastic, but there is a MARKED difference in their behaviors on those days. They stand taller, they sit straighter, their behavior is usually 100% better, they are more attentive in class.
The contrast between game days attitudes of the athletes and non-game days attitudes is HUGE.