During the periods of my life when I was a good student, I often wore a dress shirt and necktie when I wrote exams. I felt sharper, but I never knew for sure whether that had an impact on my actual performance.
Maybe it did. From WaPo, "New Study: What you wear could affect how well you work".
A recently published study from professors at the Kellogg School of Management at Northwestern University shows that when research subjects wore a scientist’s or medical doctor’s white coat, they performed better on a test known as the “Stroop test,” which asks participants to say the color of a word being shown on a flash card, rather than the word itself. The group who donned white jackets identified as lab coats performed better on conflicting flash cards, such as when the word “blue” is spelled in red letters. Those wearing the lab coats, which people typically associate with care and attentiveness, made about half as many errors as their peers.
The article also says that when the subjects were told their white coats were artists' coats, their performance did not improve. [nor did it get any worse, a relief to know, given some of my artistic tendencies!]
I expect these results are both important and yet common sense. Dressing in a way that a person thinks is consistent with or emblematic of their goals quite likely does affect their behaviour. One would not ordinarily wear a coat and tie to work in an office that emphasizes casual dress for fear of appearing officious; at the same time, a male prof might not be as effective if he showed up for class wearing argyle unitards (depending on the class being taught, of course).