The last levels that DS2 received were 4b(r), 4c(w) and 4c(m) at the end of year 4. At the average rate of progress teachers were confident that he would be level 5/6 at the end of KS2. At GCSE the prediction was A*/A etc.
He is now at the end of year 5. I had some concerns about his writing but staff dismissed them on the basis that my expectations were too high wrt english as the best he could hope for at GCSE was a C grade, with a lot of effort and support. On the other hand he should get A*/A for maths and science.
This is a total contradiction of what I was told was the case last year and would not be the prediction suggested by the assessment. The staff just say that the assessment system has changed as if this explains why there should be a different GCSE prediction 
But, this reduction of expectation at GCSE does not appear to be due the new style of assessment - year 5 sat the new SATs papers and DS2 is well suited to the format of SPAG where he displays knowledge but doesn't use it (ASD plus 11+ tuition).
I am starting to think that the assessments given before were bullshit and the school are using the introduction of new SATs to radically reduce previous predictions whilst simultaneously claiming average progress.