When we were discussing how to grade the new GCSE specifications as a department, I thought about how the exam boards do it, and tried to replicate that as much as possible; I used a normal distribution.
The premise is simple if you have some knowledge of statistics; use the mean and standard deviation from FFT targets to convert normalized test results back to a grade from 1 to 9. Provided that teaching within your department is good, the results should be fairly accurate.
I have created a spreadsheet that can convert test UMS scores to grades, given targets for a cohort. I have attached a link to view the google spreadsheet here:
You should be able to make your own copy to edit as you wish, but this is a system that could work for any subject, or potentially at Key Stage 3. It will work for any test, and could allow for collaboration between schools on sample assessment materials.
The levels given could indicate a potential grade in the topics studied for a particular test, they do not indicate a “working at” grade, and I have included cumulative results and grades to give a fuller idea of a potential overall grade.