SBG and Grades

I blogged recently about some of the issues I have with SBG when it comes to reassessments. The other issue that I did not touch upon is equally as thorny. When you are the only one doing Standards Based Grading and you have to give a percentage grade, how do you go about doing it?

The past two years, I have taking my scale and converted it to scores out of ten points.



Basically, I added 5 to each numeric score and made it a score out of 10. The first year, I felt pretty good about where grades ended up. I can't say that this year. I had 2 students who passed Algebra 2 who probably shouldn't have passed the course. I am wondering if I have my scores correlated to the appropriate grades.

In Ohio, we give students a score on their state tests based on the following 5 point scale:
Basic
Limited
Proficient
Accelerated
Advanced

Now, granted, some of the names are misnomers to me because in order to be "Proficient," you earn about 40% of the possible points on the test. Plus, the skills that are tested (at least for the Ohio Graduation Test) are from 8th through 10th grade and if it's supposed to be a graduation test, I feel it should also test 11th and 12th grade skills. However, I'm not presenting the names as an attempt to argue about the OGTs today.

BUT, I do think I need to possibly change how I grade and stay with the idea of a true 5-point scale that our state testing uses. I am struggling with how to adjust the worth. I figure to drop the "0" and work with 5 true points. Our school grading scale is:
0-65% F
66-74% D
75-84% C
85-92% B
93-100% A
We give percent scores on the report card as well as on progress reports.

The first two should be, in my mind, something along the lines of little or no knowledge and some knowledge. Neither of these scores should be passing. Since 66% is passing, I'm not totally sure how I want to break these up. One thought I have is the lowest should be 5/10 (50%) and the second lowest 6/10 (60%) or 6.5/10 (65%).

The middle score is I think too high currently at 8/10 (80%). I am thinking it should be at 7.5/10 (75%), which is the lowest C in our grading scale. However, if I do that, where do I put the second highest score? 8.5/10 (85%)? 9/10 (90%)? Do my increments really need to be equal? I still want the top score to be 10/10 (100%), but then I still have the issue of what do I do with the students who have the concepts down but make one computational error (whom I tended to give a 4.5 -> 9.5/10 (95%)) or have the idea down except for one minor conceptual error that was not specifically related to the concept being graded. So that brings me back to a 6 point scale rather than 5 points.

So many questions, so few answers. How do you adjust your SBG in a non-SBG grading world?