Step 1: Don't.
Step 2: Are you sure you absolutely positively have to assign a single number to students' product or demonstration?
Step 3: OK. I hear you. Grades are a Damocles sword under which many educators must exist. You have to feed that monster. So for real now...
Step 1: Confirm that a quality rubric is the right tool for communicating expectations and evaluating the outcomes of this particular task. The task is meaningful, authentic, and/or something that happens in world outside of "school."
Step 2: Confirm that the attributes you are evaluating are about the quality of the students' work or demonstration. If you're evaluating countable things such as 3 spelling errors, presence of a cover page, title, etc., consider a checklist or scoring scheme.
Step 2a: It's not too late. Is it possible you can communicate the student's grade through a holistic score? For example, when assessed against the rubric, the student's work or demonstration is mostly at a Level 2 and use that value to appease the grading monster? No? You need a value from 0-100? Ok. Carry on.
Step 3: Confirm that in your rubric, the third level (3) reflects your expectations, 4 is above and beyond, 2 is just below, and 1 reflects a beginner. In other words, the rubric should describe growth with the lowest level describing what a beginner does, NOT all the ways students get it wrong. To make an analogy to grading, the lowest level should reflect the qualities of just barely passing.
Step 4: Go to Roobrix.com and adjust the settings to match your minimum passing grade. The author of Roobrix.com created an algorithm based on the passing percentage you enter. So, if you as the evaluator circle all Level 1's, the student's grade is 65%, the minimum score required to pass in most schools.
Step 5: Accept that there is no real difference between a grade of 64 (just below passing) and 44 (20 points below passing). If a student hasn't met your minimum expectations when it comes time to grade, they haven't met the criteria in Level 1, their score is a 64. Any machinations to come up with an "objective" mathematical variable below 64 is fancy footwork. It's okay to let that go.
Step 6: Figure out how you're going to handle students whose products or demonstrations go beyond your expectations. Since a Quality Rubric is based on the supposition that Level 3 is our expectation and 4 goes beyond that, there’s cognitive dissonance in withholding the grade of 100% for only those who exceed expectations. In other words, if a student did what we wanted (Level 3), shouldn’t they receive a grade of 100%? To negotiate this tension, the user can configure the Roobrix.com settings so the rubric has only 3 levels, setting all 3’s as equal to 100%. If a student’s work exceeds expectations and has Level 4 traits, you can provide bonus points or consequences such as display in the community, publication, or other authentic rewards that make sense given the task and the teacher’s classroom and grading system. Additionally, if the Quality Rubric is accompanied by a checklist, the checklist can be treated as an additional dimension, with Level 3 corresponding to a fully completed checklist.
Step 7: Adjust the colored tiles to match the levels you noticed on each student's rubric. The algorithm isn't complicated and once you use it a few times, it becomes pretty clear how it's figured. You may find it help to use a blank rubric to keep track of possible configurations. For example, in a 3x4 rubric, 3 Level 3's and 1 Level 2 = 96%.
Feel free to shout at me on Twitter at @JennLCI if you have any questions!