In regard to using a rubric for assessment with Investigations, I have used a rubric along with a math portfolio in my classroom. The rubric is on a scale from four to zero. A four consists of the following items: An appropriate strategy is used effectively(strategy). The response if highly organized and well documented (organization). Responses to all parts of the prompt are effective and appropriate (communication). A correct solution is presented (solution). Efficient, accurate use of mathematics is evident throughout (mathematics. A three is basically the same items, however they are scaled down. For example, many of the same things are done, but not effectively. A two would consist of a partially correct response. A one is a strategy that is attempted or unclear. A zero is not attempt or off of the point.
In creating rubrics in the past, it helps to decide what would be expected of a four paper. List all of the criteria, and then scale it down for a three, two, etc.
I could send you a copy of the entire rubric if you would like.