What makes a good science teacher?...
Lots of other ScienceBloggers have given really good answers to this, so I'll just add one more thing. A good teacher has to know what students don't know. When I ran into problems, I was always assuming that the students had sufficient background. I think too often teachers (and for that matter, people in general) underestimate ignorance--what students know and remember. If you keep that in mind, you won't lose the class (hopefully...).
Mad rantings about politics, evolution, and microbiology. Comment policy: say what you want, but back it up with an email address. I don't like anonymous trolls.

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