It's not so much as what they SHOULD know, common-**** deals with how they unnecessary steps to get there. ******** can no longer be graded on the correct answer, but the steps they took to get that answer.
You did bring up a good point, though, you are taking the time to ensure your ******** learn.
Common-**** teaches ******** the minimum they must know, rather than teaching them to excel at achieving their goals. If, like you, me and many other families, we spend time ensuring our ******** learn the practical applications of their education, then they are ok. But to just rely on common-**** will just ensure our common substandard system of bringing ******** into the real world.