Assessment rubrics

I chose to read chapter 8 on Responding and Assessing multimodal projects (and not just because Brian was one of the authors). One of the issues that gave me pause (other than the multimodality of it all; I'm still doing my best to reconcile myself to that concept) was the discussion early on of rubrics constructed by the class.

On page 101 the text says "Creating a collaboratively constructed rubric--or using other similar instructive-assessment strategies--helps to make classroom expectations, including the newer elements of multimodal texts, more apparent for both teachers and students."

This is something I've thought about quite a lot in putting together my assignment sheet and in general about getting ready to assess a class. I'm by no means an expert on most of these multimodal concepts, so it's going to be tough for me to tell students exactly how I'm going to grade them on, for example, a film project. How systematic do I make the grading procedure? I know students have very definite ideas of fairness and want to know exactly how they're being assessed. But having the transparency of a defined rubric in which they'll see exactly how many points they get on each individual category seems a little problematic. It makes it much easier for students to quibble over every single point, for one thing. It also takes away some of our wiggle room; in general, we know what an A or a B or a C looks like, right? Or do we?