Everyone graduates from high school knowing how to read, write and do basic math (you would hope). But to be a self-sufficient adult, those skills are not enough. In fact, they're nowhere close to enough.
Advanced skills in academic areas aren't going to help young adults out of every jam they are likely to face in the next few years. Most of those predicaments probably will have nothing to do with Shakespeare, trigonometry or world history. What will they do when their cars break down or they get sick? Do they know how to navigate a job interview or a lunch with coworkers? Are they responsible with money?
Schools teach many of these skills, either directly or woven into other academic subjects. But it's up to parents to make sure their teens can take care of themselves in the world.