I found with many purchasable systems, they relied on a very basic, unfounded belief that all children make equal gains at timetabled stop-points within the year. As current teachers, we know that simply isn't true, yet in the business of proving progress, you'd be required the tick the box regardless, in order to make the algorithm give the result you needed on the analysis. I wanted a system that better reflected how children make progress in writing, while also giving leaders what they needed.
My systems works on the simple idea that you can reward children for the smaller steps in progress that they make. By awarding points 0 through 10, you can always credit the children for their inevitable progress, and the overall judgement is based on what percentage of the skills (at whatever level of capability) they are completing successfully.
Don't ask, "But how do you know whether to award them a 4 or a 5?" Use the same part of your brain that decided whether they were at or above, or a 3b or 3a. It takes a few turns, but it always has done.