But, for now…We must have that single number.

We have worked together to develop a plan.  We started by studying Classroom Assessment & Grading that Work and Transforming Classroom Grading by Robert J. Marzano.  As a team, we have analyzed student work to calibrate our understanding of the rubric and how we score student work.

In Transforming Classroom Grading we read and studied Chapter 5. Assigning Final Topic Scores and Computing Grades and Appendix D: The Power Law Formula.

We investigated the following conversions by scoring student work and then analyzing the following scales to determine which scale most closely aligns with the team’s thinking about a score out of 100 points.

We looked at this data graphically.  We wanted to see how a power function looked on the data.

Looking at Scale 1…
4 translates to 100, 3 translates to 90, 2 translates to 75, and 1 translates to 60.

It appears that a power function would fit the data.

It appears that this power function would over estimate the team’s rubric score of 2 when converted to the 100-point scale.  Would there be another function that might fit better?  Should we adjust the translations?  We tried another type of function.

This is the same data – no adjustment in the translation – but we used a logistic model rather than a power function.  Interesting, huh?

Looking at Scale 2…
4 translates to 100, 3 translates to 90, 2 translates to 75, and 1 translates to 65.

Power Function:
 Logistic Function:

Looking at Scale 3…
4 translates to 100, 3 translates to 88, 2 translates to 73, and 1 translates to 65.

Power Function:

Logistic Function:

Numerically, the logistic function more closely converts our 4-point rubric scores to our agreed upon 100-point scale translation than the power function.

You are welcome to make a copy of our 4-Point Conversion E-PLC  or 4-Point Conversion S-PLT Google spreadsheet and investigate for yourself.

This is where we are today.  We have decided which of these scales works for our teams.  We have calibrated our understanding and use of our rubrics.  We have investigated these conversion tables numerically, graphically, and analytically.  We have agreed to use the same conversion table to represent our learners’ work and progress.

This is a work in progress.  We would love to know how you translate your rubric scores to the 100-point scale.