So what about the students who turn up smelling of horses, or whatever they have been doing before flying? What about the ones wearing totally unsuitable clothing for a flying lesson -eg ehite designer jeans, high heeled boots, skimpy top showing rolls of white midriff? Or the guy expecting to fly a C152 wearing a fur lined mock flying jacket and white leather gloves? Why do we not decree a uniform for students too? dark trousers, trainers (not white) and warm pullover or sweatshirt (also dark so it does not show oil etc)?
I am in favour of wearing whatever portrays the correct image for the circumstances so if we are teaching for a professional course then the instructor and the student should look professional. But should women wear ties (I have asked this before) or does it mean they are trying to look like men? If you are doing a tailwheel or seaplane rating then jeans and jersey or flying suit may be more appropriate for the instructor and the student as the practicalities of keeping warm must prevail.