Student Assessment in the 1st Year of Modeling Physics

I'm in the middle of writing syllabi and have come to a road block. How do I explain my grading procedure? I haven't even resolved how I am to do it. I've been reading some great blog posts on the subject of standards-based grading from experienced modelers. I can see that it is so complementary to modeling instruction. I want to implement SBG as soon as I can, but don't see it happening in this first year. Having to use the school web-based reporting system requires having to set up a separate system that keeps students and parents informed. I read Brian Battaglia's blog posts from his first year of modeling. They were very encouraging and helpful. This confirms for me that I will put off SBG and focus on my modeling and not "leading the witness" in my attempts at socratic questioning. For now I am going to work on my SBG process for implementation next year and selling it to my administration and colleagues. Given the dramatic change from traditional to modeling instruction I remain in a quandary. How do I grade, categorize and weigh achievement in cognitive understanding? What does the reassessment process look like?