If you are using the Units of Study Writing program from Lucy Calkins and Teacher's College, this checklist goes hand in hand with the 3rd grade rubric. After your initial on demand assessment you can use this to track what your students know, and then at the end of the unit you can do the same with the post on demand assessment to see how they have grown. I also use this in my conferences, I take something I noticed students did below grade level in or are completely missing and look for that in their writing. If I still don't see it that gives me the teaching point for that child. I also plan small group strategy lessons on students with similar needs.