Please don’t knock the “modern Orthodox schools” My girls attended a HS on Long Island that is labeled Modern Orthodox.
The school dress code was ankle length skirts – NO EXCUSES. ALL the girls wore long skirts, no slits, no buttons, etc.
I think a problem stems from being a “Kallah Maidel” When I was in HS in Brooklyn, during the 60’s and the mini skirt era, we all dressed Tzniusdically UNTIL we turned 16. Once we became old enough to be “looked over”, our Moms dressed us fashionably with make-up and heels. And the problems began. This is not a NEW problem, this is a fashion problem !!
The girls on Long Island are NEVER told to dress up when they go to school, they are told to dress down. And while the look is somewhat sloppy, ie: long schleppy skirts with oversized sweatshirts, as mothers, we are happy with the look and the LACK of focus on fashion !!