Come now, that is blatant overstatement. When I was 18, I knew how to read, write, do calculus, use Microsoft Office, do a bit of coding, and even enough to work in a biological research lab.
The problem is most skills needed in the economy are not aligned with the skills taught in school. Is it necessary that a plumber can read Shakespeare and analyze it? Is it necessary that a nurse knows all about the Civil War? Well no, in a purely skills-based sense, their schooling was "not valuable" and they "don't know anything".