School is nothing more than a waste of time until you hit professional/graduate school, where you actually get to study exclusively stuff you're interested in and is actually useful to you.
The earlier schooling prepares you for those schools as well. But if you decide not to go into higher education, school still has given you a number of skills that you might use - reading, writing, math, and others. The point of having the earlier education as well rounded is because young kids don't necessarily know for certain what they want to do for a living, or always are changing their minds about it. But back to the original point - you would not survive college without having gone through earlier schooling. Hardly a waste of time.