Chances are you have a yearbook lying around with a few pages devoted to whatever clothing was in style at the time. The kids in these photos are inevitably the "cool" ones, and even though that term is loosely interpreted, in junior high and high school it likely applied sartorially to those who had a substantial wardrobe budget, always kept up with the latest looks, or were slightly rebellious and wore whatever grown-ups disapproved of.
This list begins at the start of the 20th century, and although the concept of "cool" didn't take on its meaning as something other than an indication of temperature, or an even temper, until the 1940s, even in the early 1900s everyone knew who the cool kids were.
Over the decades, what constitutes "cool" in clothing has changed dramatically. Any teenage guy who shows up to school in a three-piece suit today probably either has a job interview later or is rehearsing for a Wall Street career. Some early female fashions might still work, like the flapper look, if paired with combat boots, but corsets are no longer cool or comfortable. And even though this list is divided into male and female fashions, some of the clothing is actually gender-neutral, which could be the coolest trend of all.