What defines "expertise" in science teaching?

This is a question that I've been interested in for years, and is central to my current dissertation work (more on that later). Since I've built up a great PLN on twitter which includes many science teachers and science enthusiasts, I decided to pose the question to my tweeps. Here is a sample of their responses:

@gregorylouie said: @Bud_T Expertise ? Subject-Matter expertise + specific understanding of learning progressions based on research using developmental psych

@martywittrock said: @Bud_T A teacher that REALLY knows the subject matter but can explain it in common sense terms that a student can apply immediately

@mwacker said: @Bud_T Expert= experience, fresh ideas, and understanding of processes...what's your answer?

@wgraziadei said: @Bud_T expertise in sci: curious, visual, tactile, analytical, interactive, collaborative, reflective, professional practitioner/learner

@elizabethonline said: @Bud_T thorough interdisciplinary knowledge, know "why we care", excitement about the exciting stuff, and skills for remembering the tedium

Interesting ideas from folks: subject matter knowledge, understanding of student thinking, curiosity, experience, interactive nature, collaborative, reflective, communication skills, etc. I certainly can't disagree with any of these things, and I'm sure the list could go on and on.

But let me refine the question a bit for the purposes of the rest of this post: what knowledge do expert science teachers hold? I purposefully parse this from dispositions in order to try and bring the conversation into teacher education and to figure out what we, as science teacher educators, can teach in order to help prepare good beginning science teachers.

Certainly, knowledge of scientific subject matter is important. I don't think anyone would disagree with this. Two other things, which are at least hinted at in the above thoughts and are central to my dissertation work, are knowledge of specific student learning difficulties in the area being taught, and knowledge of appropriate representations of subject matter. When conceptualized within contextual knowledge, these two things along with subject matter knowledge form the essential components of pedagogical content knowledge (PCK; Shulman, 1986). For a more detailed explanation of my interpretation of this model of science teacher knowledge, please see my research proposal (Talbot, 2008).

Now I'm not saying that these are unequivocally the most important knowledge domains for a science teacher to possess, though I do believe they are very important. Further, they are things we can teach prospective science teachers in our teacher education courses. Many of us already focus on these things through the teaching and inclusion of inquiry, assessment, knowing students, etc. But, can we fully articulate why these things are important? That's something I'm working on- the 30 second "elevator speech" as one of my advisers would call it. Can you (or I) convince someone of what a highly qualified science teacher must know? I think we (science teacher educators) should all be able to do this, and further I believe we should use our voices to inform and even influence policy. 

Please let me know what you think. As always, comments are welcomed.

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New twitter responses since this was posted:

@BeckyFisher 73 said: @Bud_T I think understanding misconceptions and being able to unteach them is huge for a science teacher.

@chrisludwig said: @Bud_T A highly qualified science teacher must know how to tell good science from bad and be able to teach students to tell the difference

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References

Shulman, L. S. (1986). Those who understand: Knowledge growth in teaching.Educational Researcher, 15(2), 4-14.

Talbot, R. M. (2008). Measuring science teacher knowledge: Domain-general or domain-specific? (Research proposal). Boulder, CO: University of Colorado at Boulder.

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