Nobody worried about "teenagers" prior to the 1940s. In fact, they did not exist. But in the fifty years since the last world war, when the term was coined, teenagers have had an enormous impact on American culture. They have reshaped our language, our music, our clothes. They have changed forever the way we respond to authority. They have become a $200 billion consumer group avidly courted by marketers. And they have changed our culture, which will never again treat their demographic group merely as young adults. How did this influential group come into being, evolving from adults in training who went to work at age thirteen or so (if they could) and then disappeared into the general population? This is the first book to tell that story.