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.
I graduated high school with a 2.4 GPA. If you take out the math classes, it was a 1.6 GPA. Nonetheless, I flourished in college, graduating with a 3.4 GPA.
I can honestly say that, other than the math (which I was interested in), I didn't learn a damn thing in high school. So much for well-roundedness.
People learn what they want (or need) to learn. I never did any high school writing assignments for english classes. When writing became a necessity in appraising and physics lab, I had little trouble picking it up. To summarize: the english classes did no good because I wasn't interested. Requiring the skill for a higher lever of school and job forced me to learn the skill--much less painfully than sitting through all those classes.