Mary Worell, an American journalist-turned-teacher who is currently working in the Netherlands, finds it significant that Dutch educators, including administrators, tend to dress very informally:
I realized that this casualness toward dress code was indicative of something deeper in the culture of the school and the attitude toward the teachers. They are considered professionals and treated as such. It's as if someone said "Yes, I know you're a professional and I don't need you to wear black pumps and suit pants to prove it."...
...Overall the school culture itself seems to lead toward a mutual respect among colleagues and an understanding that whether one wears jeans or a suit doesn't mean one is a better or worse teacher. Effectiveness isn't tied to your tie. Leadership isn't lost by leaving your collar unbottoned.
It’s an interesting observation because, on the other hand, we’ve definitely heard some U.S. teachers complain that the lax attire of their younger colleagues is paramount to a decline in professional standards. But then, I suppose you also have to distinguish, at least in the U.S. if not in the Netherlands, between casual dress and inappropriate dress.