The always-thoughtful Diane Ravitch has an interesting piece in the Boston Globe where she takes the 21st Century Skills movement to task. Her argument is that while critical thinking is important, you can't think critically unless you have the knowledge upon which to base your thinking. Therefore, rather than try to explicity teach "critical thinking" the same we would, say, teach the parts of a cell, we should focus on the core knowledge that will provide a foundation for such thinking.
I'd say that she's at least 85% right. Assuming (and this seems like a possibility at least) that she doesn't object to focusing on critical thinking after the core knowledge is in place, she may even be 100% right. The fact is, without facts, we don't really have anything to think critically about. We can spin the wheels in the brain, but ultimately we won't come up with anything unless we actually know something to begin with. (The one possible exception might be Descartes' "I think therefore I am.")
That said, I think that there is a value in lessons on thinking critically and the connections and flaws that we can develop through that process.
In high school, I was a member of the debate team, which made me probably the coolest kid in the whole school. The first step to each debate topic was to stock up on facts and figures and the arguments of the past. That was the core knowledge part of the thing. But in the end, that wasn't enough. It wasn't until my senior year when I'd really absorbed the formalized way of thinking and arguing that I was able to start winning debate tournaments. Until that point - until I'd really started to learn what critical thinking meant in that context - I was well-prepared, but ultimately ineffectual.
So the balance must be found. Certainly the base of knowledge is critical, but so too is a systemitized way of thinking. Without both, neither is much good.
P.S. Could Teach for America be reading this blog? Looks like they're working more on professional development for their teachers. Sounds familiar.