Back in high school, I know I envied my friends who weren't forced to work or didn't have to. Instead of rushing like a chicken with their head cut off after school, they always had a leisurely afternoon ahead. Although it sounded really envious at the time, not having a job in high school probably wouldn't have prepared me for all the challenges ahead in college - in the work force and otherwise.
During my various side jobs in high school I learned how to have an overall professionalism about having a job; a skill I found was applicable in college academics, networking and trying to set up opportunities for myself in college. Whether it was how to email a professor or simply recognizing a good networking opportunity, having job experience before setting foot on a college campus seemed imperative.
Having prior job experience also taught me how to work on a project with people I don't know all that well like classmates, for example. That air of professionalism was easy for me to draw on in determining how to effectively work with people I didn't know personally. On-the-job skills trained me to think on my feet in collaboration with a coworker to achieve a time sensitive goal.
Another important skill that having a job before college? Managing money, AKA the most valuable skill to have in college. Knowing the value of a dollar really keeps me in check from buying things I just simply can't afford, and how to save for the things I know I really need. Distinguishing a want from a need is something that happens when you have a job in high school. It's arguably the best time to learn that lesson because you can learn without having the real stress of owing money every month.
Without prior job experience, I feel a lot of incoming college students could get themselves into a lot of trouble financially. Maybe someone will convince them to open a credit card or they'll spend money they don't have. Also, when it's time to go after the job you want, you need to know how, and having previous job experience gives you guidelines to follow. It's a good idea to get to feel what it's like to make money, and conversely what it's like to not make any money, for it creates an accurate and gratifying view of money. It'll set your expectations to know that everything comes at a price and it should be earned. It's never a bad idea to build professional skills early on in life. The more practice you allow yourself to have, the more prepared you'll be when it's actually game time.