While some of us might be able to remember students protesting their school's dress code in years past, it's probably fair to say that it's happening more frequently and in much greater numbers nowadays.
The reasons why depend on the school in question, but common criticisms of school dress codes concern their tendency to police the way girls dress more stringently than their male counterparts. Another common issue concerns the subjective and nebulous excuse that whatever outfit a school happens to dislike is a "distraction."
Even when a dress code is clearly defined and explained, there's still some room for interpretation as to which outfits are considered appropriate or inappropriate depending on who is seeing them.
And that seems to be at the heart of one parent's confrontation with a school principal after her daughter was disallowed from returning to class due to her outfit.