When I went to high school, it was in preparation for me to go to college. I was going to go to college so that I could be a professional. Being a professional meant I'd be a real adult. For my students, high school isn't just college preparation. Some of my kids won't go to college. That's okay. College isn't for everyone and we certainly need skilled trade workers. So, if you're not planning on college, what is high school for?
School is compulsory to age sixteen in my state. That means, until you are sixteen or graduate, you are required to learn. But why? What good is school for a kid that wants to work on cars for the rest of his life? What good is school for a kid who wants to be a tattoo artist? What good is school for a kid who wants to be a plumber, electrician or any other skilled job?
School is a lot of good to those kids. First, in order to engage in most entertainment forms, you need at least a mild working knowledge of history. Math is needed for any financial dealings. No, you don't use algebra every day. However, knowing algebra means that you can use formulas and can hopefully figure out things like APR or APY in your financial plans. I'm sure it goes without saying that a working knowledge of your anatomy is a good idea, so science is good, too.
What about reading? English is useful for a variety of reasons. Reading contracts, arguing your point of view and enjoying films by being able to follow simple plots are all important and useful in real life. People who can't read well or argue without violence are at a severe disadvantage in most adult dealings.
Aside from all of the skills learned in school, students also learn the value of manners, timeliness and presenting themselves. It's rude to talk while others are talking. Turning assignments in on time is good. Dressing appropriately for the situation is required in most professions. Students who excel on the behavior and compliance side of education will be good employees who will keep their jobs easier. Being aggressive and disrespectful in the real world earns one a pink slip rather than a failing grade.
Whenever students complain about going to school being worthless, I always go over these points with them. Most agree that they'd like to have a job, car and house in their future. All of these things require at least passing high school, if for no other reason than the skills learned.