At the school I taught at it was expected of the instructors to wear ties in the winter time but when summer rolled around we wore a summer shirt with open neck for practical reasons in the hot SA sun.
Partly this was to set the standard. As an organisation we are in the business of teaching both private and professional pilots. how will they know what is accepted by the industry both in terms of dress and behaviour if the example is not set by those people who they look up to.
The students do not have a uniform as such but wear flying overalls. They even wear eppaulettes that show were in the course they have progressed to. Not because it's funny or pretentious, but even at that point to get used to, on a small scale, what will be expected of them as profesional pilots and job seekers.
my 2cents worth!