Be Skeptical . . . But Not Dismissive
As a middle school librarian, I find that many students fall into one of two categories: they believe almost everything, or they believe almost nothing. Everything is true, or everything's a lie. Facts are self-evident, or facts are impossible to divine. Reality is absolute, or reality is whatever you want it to be. It's difficult to teach (or convince) someone how to walk a line between these two extremes; to be skeptical without being entirely dismissive of even the possibility of credibility.
15 years into my career as a librarian, I see more and more students falling into the second category. This current generation has been taught repeatedly that they can't trust anything on the internet or in the media. They also hear from the adults around them that all politicians (and, by extension, all people in positions of power) lie--and, what's more, that lying is normal and inevitable.
I think sometimes we K-12 librarians focus too much on teaching students strategies for evaluating information and resources--the