When I got hired for my first job out of college as a research assistant in the genetics department at Children's Hospital Medical Center in Cincinnati I was told the main component of my job was to run a process called PCR. I had learned, briefly, about the polymerase chain reaction while in undergrad but had no idea where to begin running this procedure on my own. I nervously asked if I was expected to know how to do this on my own, and my boss said of course not, that he would train me. This was the "real world" wasn't it? This is what we teachers preach to our students all the time, isn't it? Wasn't this why I went to school, to learn things that I would use in a future job? Well, it turns out I was only expected to be able to learn something new, not necessarily utilize everything I has learned in each class.
I am not in any way saying that no content should be taught. Learning conceptually difficult material is beneficial, it builds confidence, and develops a sense if curiosity. Being able to critically think about new material is aided by prior knowledge, but what is that essential knowledge in each core area? I would argue that we need to spend significantly less time on content and more on critical thinking. Teach the basics, give students the opportunity to think, challenge them with difficult material, and then make them think some more.
My boss at CHMCC didn't care that I wasn't walking into the lab with the ability to run a PCR machine on my own. What he cared about was whether or not I could learn quickly, and understand the importance of each step of the PCR procedure. Content matters, but if I had an endless supply of content facts, but no ability to think beyond those facts, what good would they be? Teach kids how to think, how to be curious, and do so in the context of your core subject area, and they'll be successful in whatever they choose.